diff --git a/Source/Core/IO/DoomMapSetIO.cs b/Source/Core/IO/DoomMapSetIO.cs
index 5878a39..7a6d92e 100644
--- a/Source/Core/IO/DoomMapSetIO.cs
+++ b/Source/Core/IO/DoomMapSetIO.cs
@@ -35,11 +35,6 @@ namespace CodeImp.DoomBuilder.IO
         #endregion
 
         #region ================== Variables
-        protected Dictionary<int, int[]> threeDFloorTypes;
-        protected Dictionary<int, int[]> slopeTypes;
-        protected Dictionary<int, int[]> slopeCopyTypes;
-        protected Dictionary<int, int[]> vertexSlopeTypes;
-        protected Dictionary<int, float> translucentLineTypes;
         #endregion
 
         #region ================== Constructor / Disposer
@@ -52,6 +47,8 @@ namespace CodeImp.DoomBuilder.IO
             slopeCopyTypes = new Dictionary<int, int[]>() { { 118, new int[2] { -1, -1 } } };
             vertexSlopeTypes = new Dictionary<int, int[]>() { };
             translucentLineTypes = new Dictionary<int, float>() { { 208, -1.0f } };
+            unflippableTypes = new List<int>();
+            startTypes = new List<int>();
         }
 
         #endregion
@@ -100,19 +97,12 @@ namespace CodeImp.DoomBuilder.IO
 		public override int MaxThingAngle { get { return short.MaxValue; } }
 		public override int MinThingAngle { get { return short.MinValue; } }
 		public override Dictionary<MapElementType, Dictionary<string, UniversalType>> UIFields { get { return uifields; } } //mxd
-        public override Dictionary<int, int[]> ThreeDFloorTypes { get { return threeDFloorTypes; } }
-        public override Dictionary<int, int[]> SlopeTypes { get { return slopeTypes; } }
-        public override Dictionary<int, int[]> SlopeCopyTypes { get { return slopeCopyTypes; } }
-        public override Dictionary<int, int[]> VertexSlopeTypes { get { return vertexSlopeTypes; } }
-        public override Dictionary<int, float> TranslucentLineTypes { get { return translucentLineTypes; } }
         public override int SlopeVertexType { get { return 9500; } }
         public override int Custom3DFloorType { get { return 160; } }
         public override int ColormapType { get { return -1; } }
         public override int FlatAlignmentType { get { return -1; } }
         public override int AxisType { get { return -1; } }
         public override int AxisTransferLineType { get { return -1; } }
-
-
         #endregion
 
         #region ================== Reading
diff --git a/Source/Core/IO/HexenMapSetIO.cs b/Source/Core/IO/HexenMapSetIO.cs
index 7ea2b19..4506006 100644
--- a/Source/Core/IO/HexenMapSetIO.cs
+++ b/Source/Core/IO/HexenMapSetIO.cs
@@ -35,11 +35,6 @@ namespace CodeImp.DoomBuilder.IO
         #endregion
 
         #region ================== Variables
-        protected Dictionary<int, int[]> threeDFloorTypes;
-        protected Dictionary<int, int[]> slopeTypes;
-        protected Dictionary<int, int[]> slopeCopyTypes;
-        protected Dictionary<int, int[]> vertexSlopeTypes;
-        protected Dictionary<int, float> translucentLineTypes;
         #endregion
 
         #region ================== Constructor / Disposer
@@ -52,6 +47,8 @@ namespace CodeImp.DoomBuilder.IO
             slopeCopyTypes = new Dictionary<int, int[]>() { { 118, new int[2] { -1, -1 } } };
             vertexSlopeTypes = new Dictionary<int, int[]>() { };
             translucentLineTypes = new Dictionary<int, float>() { { 208, -1.0f } };
+            unflippableTypes = new List<int>();
+            startTypes = new List<int>();
         }
 
         #endregion
@@ -100,18 +97,12 @@ namespace CodeImp.DoomBuilder.IO
 		public override int MaxThingAngle { get { return short.MaxValue; } }
 		public override int MinThingAngle { get { return short.MinValue; } }
 		public override Dictionary<MapElementType, Dictionary<string, UniversalType>> UIFields { get { return uifields; } } //mxd
-        public override Dictionary<int, int[]> ThreeDFloorTypes { get { return threeDFloorTypes; } }
-        public override Dictionary<int, int[]> SlopeTypes { get { return slopeTypes; } }
-        public override Dictionary<int, int[]> SlopeCopyTypes { get { return slopeCopyTypes; } }
-        public override Dictionary<int, int[]> VertexSlopeTypes { get { return vertexSlopeTypes; } }
-        public override Dictionary<int, float> TranslucentLineTypes { get { return translucentLineTypes; } }
         public override int SlopeVertexType { get { return 9500; } }
         public override int Custom3DFloorType { get { return 160; } }
         public override int ColormapType { get { return -1; } }
         public override int FlatAlignmentType { get { return -1; } }
         public override int AxisType { get { return -1; } }
         public override int AxisTransferLineType { get { return -1; } }
-
         #endregion
 
         #region ================== Reading
diff --git a/Source/Core/IO/IMapSetIO.cs b/Source/Core/IO/IMapSetIO.cs
index a377225..a5d5d7c 100644
--- a/Source/Core/IO/IMapSetIO.cs
+++ b/Source/Core/IO/IMapSetIO.cs
@@ -81,5 +81,7 @@ namespace CodeImp.DoomBuilder.IO
         int FlatAlignmentType { get; }
         int AxisType { get; }
         int AxisTransferLineType { get; }
+        List<int> UnflippableTypes { get; }
+        List<int> StartTypes { get; }
     }
 }
diff --git a/Source/Core/IO/MapSetIO.cs b/Source/Core/IO/MapSetIO.cs
index 426b043..c0a468c 100644
--- a/Source/Core/IO/MapSetIO.cs
+++ b/Source/Core/IO/MapSetIO.cs
@@ -45,11 +45,18 @@ namespace CodeImp.DoomBuilder.IO
 		//mxd
 		protected Dictionary<MapElementType, Dictionary<string, UniversalType>> uifields;
 
-		#endregion
+        protected Dictionary<int, int[]> threeDFloorTypes;
+        protected Dictionary<int, int[]> slopeTypes;
+        protected Dictionary<int, int[]> slopeCopyTypes;
+        protected Dictionary<int, int[]> vertexSlopeTypes;
+        protected Dictionary<int, float> translucentLineTypes;
+        protected List<int> unflippableTypes;
+        protected List<int> startTypes;
+        #endregion
 
-		#region ================== Properties
+        #region ================== Properties
 
-		public abstract int MaxSidedefs { get; }
+        public abstract int MaxSidedefs { get; }
 		public abstract int MaxVertices { get; }
 		public abstract int MaxLinedefs { get; }
 		public abstract int MaxSectors { get; }
@@ -91,19 +98,19 @@ namespace CodeImp.DoomBuilder.IO
 		public abstract int MaxThingAngle { get; }
 		public abstract int MinThingAngle { get; }
 		public abstract Dictionary<MapElementType, Dictionary<string, UniversalType>> UIFields { get; } //mxd
-        public abstract Dictionary<int, int[]> ThreeDFloorTypes { get; }
-        public abstract Dictionary<int, int[]> SlopeTypes { get; }
-        public abstract Dictionary<int, int[]> SlopeCopyTypes { get; }
-        public abstract Dictionary<int, int[]> VertexSlopeTypes { get; }
-        public abstract Dictionary<int, float> TranslucentLineTypes { get; }
+        public Dictionary<int, int[]> ThreeDFloorTypes { get { return threeDFloorTypes; } }
+        public Dictionary<int, int[]> SlopeTypes { get { return slopeTypes; } }
+        public Dictionary<int, int[]> SlopeCopyTypes { get { return slopeCopyTypes; } }
+        public Dictionary<int, int[]> VertexSlopeTypes { get { return vertexSlopeTypes; } }
+        public Dictionary<int, float> TranslucentLineTypes { get { return translucentLineTypes; } }
         public abstract int SlopeVertexType { get; }
         public abstract int Custom3DFloorType { get; }
         public abstract int ColormapType { get; }
         public abstract int FlatAlignmentType { get; }
         public abstract int AxisType { get; }
         public abstract int AxisTransferLineType { get; }
-
-
+        public List<int> UnflippableTypes { get { return unflippableTypes; } }
+        public List<int> StartTypes { get { return startTypes; } }
         #endregion
 
         #region ================== Constructor / Disposer
diff --git a/Source/Core/IO/SRB2MapSetIO.cs b/Source/Core/IO/SRB2MapSetIO.cs
index d4df6fb..6213358 100644
--- a/Source/Core/IO/SRB2MapSetIO.cs
+++ b/Source/Core/IO/SRB2MapSetIO.cs
@@ -143,6 +143,9 @@ namespace CodeImp.DoomBuilder.IO
                 { 908, 0.1f },
             };
 
+            unflippableTypes = new List<int>() { 604, 605, 606, 607, 608, 609, 1700, 1701, 1702, 1704, 1705, 1713 };
+
+            startTypes = new List<int>() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35 };
         }
 
         #endregion
diff --git a/Source/Core/IO/UniversalMapSetIO.cs b/Source/Core/IO/UniversalMapSetIO.cs
index b033b04..1caedb1 100644
--- a/Source/Core/IO/UniversalMapSetIO.cs
+++ b/Source/Core/IO/UniversalMapSetIO.cs
@@ -38,11 +38,6 @@ namespace CodeImp.DoomBuilder.IO
         #endregion
 
         #region ================== Variables
-        protected Dictionary<int, int[]> threeDFloorTypes;
-        protected Dictionary<int, int[]> slopeTypes;
-        protected Dictionary<int, int[]> slopeCopyTypes;
-        protected Dictionary<int, int[]> vertexSlopeTypes;
-        protected Dictionary<int, float> translucentLineTypes;
         #endregion
 
         #region ================== Constructor / Disposer
@@ -57,6 +52,9 @@ namespace CodeImp.DoomBuilder.IO
                 slopeCopyTypes = new Dictionary<int, int[]>() { { 118, new int[2] { -1, -1 } } };
                 vertexSlopeTypes = new Dictionary<int, int[]>() { };
                 translucentLineTypes = new Dictionary<int, float>() { { 208, -1.0f } };
+                unflippableTypes = new List<int>();
+                startTypes = new List<int>();
+
                 // Make configuration
                 Configuration config = new Configuration();
 				
@@ -150,18 +148,12 @@ namespace CodeImp.DoomBuilder.IO
 		public override int MaxThingAngle { get { return int.MaxValue; } }
 		public override int MinThingAngle { get { return int.MinValue; } }
 		public override Dictionary<MapElementType, Dictionary<string, UniversalType>> UIFields { get { return uifields; } } //mxd
-        public override Dictionary<int, int[]> ThreeDFloorTypes { get { return threeDFloorTypes; } }
-        public override Dictionary<int, int[]> SlopeTypes { get { return slopeTypes; } }
-        public override Dictionary<int, int[]> SlopeCopyTypes { get { return slopeCopyTypes; } }
-        public override Dictionary<int, int[]> VertexSlopeTypes { get { return vertexSlopeTypes; } }
-        public override Dictionary<int, float> TranslucentLineTypes { get { return translucentLineTypes; } }
         public override int SlopeVertexType { get { return 9500; } }
         public override int Custom3DFloorType { get { return 160; } }
         public override int ColormapType { get { return -1; } }
         public override int FlatAlignmentType { get { return -1; } }
         public override int AxisType { get { return -1; } }
         public override int AxisTransferLineType { get { return -1; } }
-
         #endregion
 
         #region ================== Reading
diff --git a/Source/Core/Map/Thing.cs b/Source/Core/Map/Thing.cs
index 6a8f3c0..770efa3 100644
--- a/Source/Core/Map/Thing.cs
+++ b/Source/Core/Map/Thing.cs
@@ -125,12 +125,11 @@ namespace CodeImp.DoomBuilder.Map
             get
             {
                 ThingTypeInfo ti = General.Map.Data.GetThingInfo(Type);
-                return (ti.Hangs && !IsReverse) || (!ti.Hangs && IsReverse);
+                return ti.Hangs ^ IsReverse;
             }
         }
-        public bool IsReverse { get { return General.Map.SRB2 && IsFlagSet("2"); } }
-
-
+        public bool IsReverse { get { return General.Map.SRB2 && !Unflippable && IsFlagSet("2"); } }
+        public bool Unflippable { get { return General.Map.FormatInterface.UnflippableTypes.Contains(Type); } }
         #endregion
 
         #region ================== Constructor / Disposer