diff --git a/src/gl/system/gl_interface.cpp b/src/gl/system/gl_interface.cpp
index e24ac553b2..dcde3f006a 100644
--- a/src/gl/system/gl_interface.cpp
+++ b/src/gl/system/gl_interface.cpp
@@ -324,7 +324,10 @@ void gl_LoadExtensions()
 		FUDGE_FUNC(glBindRenderbuffer, EXT);
 		FUDGE_FUNC(glCheckFramebufferStatus, EXT);
 	}
-	gl_legacy_mode = gl.legacyMode;
+
+	UCVarValue value;
+	value.Bool = gl.legacyMode;
+	gl_legacy_mode.ForceSet (value, CVAR_Bool);
 }
 
 //==========================================================================
diff --git a/src/gl/system/gl_swframebuffer.cpp b/src/gl/system/gl_swframebuffer.cpp
index 665b23d385..c0ed432117 100644
--- a/src/gl/system/gl_swframebuffer.cpp
+++ b/src/gl/system/gl_swframebuffer.cpp
@@ -207,12 +207,15 @@ OpenGLSWFrameBuffer::OpenGLSWFrameBuffer(void *hMonitor, int width, int height,
 	const char *glversion = (const char*)glGetString(GL_VERSION);
 	bool isGLES = (glversion && strlen(glversion) > 10 && memcmp(glversion, "OpenGL ES ", 10) == 0);
 
+	UCVarValue value;
 	// GL 3.0 is mostly broken on MESA drivers which really are the only relevant case here that doesn't fulfill the requirements based on version number alone.
 #ifdef _WIN32
-	gl_legacy_mode = !ogl_IsVersionGEQ(3, 0);
+	value.Bool = !ogl_IsVersionGEQ(3, 0);
 #else
-	gl_legacy_mode = !ogl_IsVersionGEQ(3, 1);
+	value.Bool = !ogl_IsVersionGEQ(3, 1);
 #endif
+	gl_legacy_mode.ForceSet (value, CVAR_Bool);
+
 	if (!isGLES && ogl_IsVersionGEQ(3, 0) == 0)
 	{
 		Printf("OpenGL acceleration requires at least OpenGL 3.0. No Acceleration will be used.\n");
diff --git a/src/p_map.cpp b/src/p_map.cpp
index 66becf1fe5..0aa3b58ad2 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -5884,7 +5884,10 @@ bool P_AdjustFloorCeil(AActor *thing, FChangePosition *cpos)
 	}
 
 	bool isgood = P_CheckPosition(thing, thing->Pos(), tm);
-	if (!(thing->flags4 & MF4_ACTLIKEBRIDGE))
+
+	// This is essentially utterly broken because it even uses the return from a failed P_CheckPosition but the entire logic will break down if that isn't done.
+	// However, if tm.floorz is greater than tm.ceilingz we have a real problem that needs to be dealt with exolicitly.
+	if (!(thing->flags4 & MF4_ACTLIKEBRIDGE) && tm.floorz <= tm.ceilingz)
 	{
 		thing->floorz = tm.floorz;
 		thing->ceilingz = tm.ceilingz;
diff --git a/src/scripting/vm/vm.h b/src/scripting/vm/vm.h
index 9ebc86f003..765ba45552 100644
--- a/src/scripting/vm/vm.h
+++ b/src/scripting/vm/vm.h
@@ -579,7 +579,7 @@ class AActor;
 //   callingstate - State this action was called from
 #define PARAM_ACTION_PROLOGUE(type) \
 	PARAM_PROLOGUE; \
-	PARAM_OBJECT	 (self, AActor); \
+	PARAM_OBJECT_NOT_NULL (self, AActor); \
 	PARAM_OBJECT (stateowner, type) \
 	PARAM_POINTER  (stateinfo, FStateParamInfo) \
 
@@ -588,12 +588,12 @@ class AActor;
 
 #define PARAM_SELF_PROLOGUE(type) \
 	PARAM_PROLOGUE; \
-	PARAM_OBJECT(self, type);
+	PARAM_OBJECT_NOT_NULL(self, type);
 
 // for structs we cannot do a class validation
 #define PARAM_SELF_STRUCT_PROLOGUE(type) \
 	PARAM_PROLOGUE; \
-	PARAM_POINTER(self, type);
+	PARAM_POINTER_NOT_NULL(self, type);
 
 class PFunction;
 
diff --git a/src/v_draw.cpp b/src/v_draw.cpp
index 49d23250e2..b60c17616f 100644
--- a/src/v_draw.cpp
+++ b/src/v_draw.cpp
@@ -1060,7 +1060,7 @@ void DCanvas::Dim(PalEntry color, float damount, int x1, int y1, int w, int h)
 			h -= (cliptop - y1);
 			y1 = cliptop;
 		}
-		if (h > clipheight) w = clipheight;
+		if (h > clipheight) h = clipheight;
 		if (h <= 0) return;
 	}
 	DoDim(color, damount, x1, y1, w, h);