diff --git a/Source/p_doors.c b/Source/p_doors.c
index 13748b73..88812735 100644
--- a/Source/p_doors.c
+++ b/Source/p_doors.c
@@ -449,9 +449,18 @@ int EV_VerticalDoor(line_t *line, mobj_t *thing)
   sec = sides[line->sidenum[1]].sector;
 
   // if door already has a thinker, use it
-  if (sec->ceilingdata)      //jff 2/22/98
+  door = sec->ceilingdata; //jff 2/22/98
+
+  // [FG] DR doors corrupt other actions
+  // http://prboom.sourceforge.net/mbf-bugs.html
+  if (demo_compatibility)
+  {
+    if (!door) door = sec->floordata;
+    if (!door) door = sec->lightingdata;
+  }
+
+  if (door)      //jff 2/22/98
     {
-      door = sec->ceilingdata; //jff 2/22/98
       switch(line->special)
         {
         case  1: // only for "raise" doors, not "open"s
@@ -466,7 +475,21 @@ int EV_VerticalDoor(line_t *line, mobj_t *thing)
               if (!thing->player)
                 return 0;           // JDC: bad guys never close doors
 
+              // [FG] DR doors corrupt other actions
+              // http://prboom.sourceforge.net/mbf-bugs.html
+              if (door->thinker.function == T_VerticalDoor || !demo_compatibility)
+              {
               door->direction = -1; // start going down immediately
+              }
+              else if (door->thinker.function == T_PlatRaise)
+              {
+                plat_t *plat = (plat_t *) door;
+                plat->wait = -1;
+              }
+              else
+              {
+                door->direction = -1;
+              }
             }
           return 1;
         }
diff --git a/Source/p_floor.c b/Source/p_floor.c
index a8a9dcbc..0fd9df51 100644
--- a/Source/p_floor.c
+++ b/Source/p_floor.c
@@ -692,6 +692,24 @@ int EV_DoChange
 // Returns true if any thinkers are created
 //
 
+// [FG] Compatibility bug in EV_BuildStairs
+// http://prboom.sourceforge.net/mbf-bugs.html
+
+static int P_FindSectorFromLineTag_Vanilla (const line_t* line, int start)
+{
+    int i;
+
+    for (i=start+1;i<numsectors;i++)
+	if (sectors[i].tag == line->tag)
+	    return i;
+
+    return -1;
+}
+
+int (*P_FindSectorFromLineTag_BuildStairs)(const line_t* line, int start);
+
+#define STAIRS_UNINITIALIZED_CRUSH_FIELD_VALUE 10
+
 int EV_BuildStairs
 ( line_t*       line,
   stair_e       type )
@@ -716,8 +734,14 @@ int EV_BuildStairs
   secnum = -1;
   rtn = 0;
 
+// [FG] Compatibility bug in EV_BuildStairs
+// http://prboom.sourceforge.net/mbf-bugs.html
+  P_FindSectorFromLineTag_BuildStairs = demo_compatibility ?
+                                        P_FindSectorFromLineTag_Vanilla :
+                                        P_FindSectorFromLineTag;
+
   // start a stair at each sector tagged the same as the linedef
-  while ((secnum = P_FindSectorFromLineTag(line,secnum)) >= 0)
+  while ((secnum = P_FindSectorFromLineTag_BuildStairs(line,secnum)) >= 0)
   {
     sec = &sectors[secnum];
               
@@ -744,12 +768,18 @@ int EV_BuildStairs
         stairsize = 8*FRACUNIT;
         if (!demo_compatibility)
           floor->crush = false; //jff 2/27/98 fix uninitialized crush field
+        // [FG] initialize crush field
+        else
+          floor->crush = STAIRS_UNINITIALIZED_CRUSH_FIELD_VALUE;
         break;
       case turbo16:
         speed = FLOORSPEED*4;
         stairsize = 16*FRACUNIT;
         if (!demo_compatibility)
           floor->crush = true;  //jff 2/27/98 fix uninitialized crush field
+        // [FG] initialize crush field
+        else
+          floor->crush = STAIRS_UNINITIALIZED_CRUSH_FIELD_VALUE;
         break;
     }
     floor->speed = speed;
@@ -809,12 +839,17 @@ int EV_BuildStairs
         //jff 2/27/98 fix uninitialized crush field
         if (!demo_compatibility)
           floor->crush = type==build8? false : true;
+        // [FG] initialize crush field
+        else
+          floor->crush = STAIRS_UNINITIALIZED_CRUSH_FIELD_VALUE;
         ok = 1;
         break;
       }
     } while(ok);      // continue until no next step is found
 
-    if (!comp[comp_stairs])      // killough 10/98: compatibility option
+    // [FG] Compatibility bug in EV_BuildStairs
+    // http://prboom.sourceforge.net/mbf-bugs.html
+    if (!comp[comp_stairs] && !demo_compatibility)      // killough 10/98: compatibility option
       secnum = osecnum;          //jff 3/4/98 restore loop index
   }
   return rtn;