From dc054f767b414885a03bac8c3428cc8e013f5934 Mon Sep 17 00:00:00 2001
From: MaxED <j.maxed@gmail.com>
Date: Thu, 7 Jul 2016 11:20:28 +0000
Subject: [PATCH] On second thought, previous fix should be applied more
 selectively.

---
 .../ClassicModes/EditSelectionMode.cs           | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/Source/Plugins/BuilderModes/ClassicModes/EditSelectionMode.cs b/Source/Plugins/BuilderModes/ClassicModes/EditSelectionMode.cs
index 51f8430..e92ec98 100644
--- a/Source/Plugins/BuilderModes/ClassicModes/EditSelectionMode.cs
+++ b/Source/Plugins/BuilderModes/ClassicModes/EditSelectionMode.cs
@@ -1035,11 +1035,26 @@ namespace CodeImp.DoomBuilder.BuilderModes
 		// This flips all linedefs in the selection (used for mirroring)
 		private void FlipLinedefs()
 		{
+			//mxd. Check if we need to flip sidedefs
+			bool flipsides = false;
+			HashSet<Linedef> selectedlineshash = new HashSet<Linedef>(selectedlines);
+			foreach(Vertex v in selectedvertices)
+			{
+				foreach(Linedef l in v.Linedefs)
+				{
+					if(!selectedlineshash.Contains(l))
+					{
+						flipsides = true;
+						break;
+					}
+				}
+			}
+
 			// Flip linedefs
 			foreach(Linedef ld in selectedlines)
 			{
 				ld.FlipVertices();
-				ld.FlipSidedefs(); //mxd
+				if(flipsides) ld.FlipSidedefs(); //mxd
 			}
 			
 			// Done