diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 53fd1bfa373..3fd0812338c 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -8207,6 +8207,10 @@ BlendFileData *blo_read_file_internal(FileData *fd, BlendReadError *error_r)
 			bhead = read_libblock(fd, fd->mainlist.last, bhead, LIB_READ+LIB_EXTERN, NULL);
 			break;
 			
+			/* in 2.50+ files, the file identifier for screens is patched, forward compatibility */
+		case ID_SCRN:
+			bhead->code= ID_SCR;
+			/* deliberate pass on to default */
 		default:
 			bhead = read_libblock(fd, bfd->main, bhead, LIB_LOCAL, NULL);
 		}
diff --git a/source/blender/blenloader/intern/writefile.c b/source/blender/blenloader/intern/writefile.c
index d84211411fa..96611b6fa9d 100644
--- a/source/blender/blenloader/intern/writefile.c
+++ b/source/blender/blenloader/intern/writefile.c
@@ -1620,7 +1620,8 @@ static void write_screens(WriteData *wd, ListBase *scrbase)
 	while(sc) {
 		
 		/* write LibData */
-		writestruct(wd, ID_SCR, "Screen", 1, sc);
+		/* in 2.50+ files, the file identifier for screens is patched, forward compatibility */
+		writestruct(wd, ID_SCRN, "Screen", 1, sc);
 		if (sc->id.properties) 
 			IDP_WriteProperty(sc->id.properties, wd);
 
diff --git a/source/blender/makesdna/DNA_ID.h b/source/blender/makesdna/DNA_ID.h
index ea9f64cc26c..3ad2ae48d53 100644
--- a/source/blender/makesdna/DNA_ID.h
+++ b/source/blender/makesdna/DNA_ID.h
@@ -174,6 +174,7 @@ typedef struct PreviewImage {
 #define ID_KE		MAKE_ID2('K', 'E')
 #define ID_WO		MAKE_ID2('W', 'O')
 #define ID_SCR		MAKE_ID2('S', 'R')
+#define ID_SCRN		MAKE_ID2('S', 'N')
 #define ID_VF		MAKE_ID2('V', 'F')
 #define ID_TXT		MAKE_ID2('T', 'X')
 #define ID_SO		MAKE_ID2('S', 'O')
diff --git a/source/blender/makesdna/DNA_windowmanager_types.h b/source/blender/makesdna/DNA_windowmanager_types.h
index 05d4bc10486..0684503b2b2 100644
--- a/source/blender/makesdna/DNA_windowmanager_types.h
+++ b/source/blender/makesdna/DNA_windowmanager_types.h
@@ -71,7 +71,7 @@ typedef struct wmWindowManager {
 	ListBase screenkeymap;
 	ListBase uikeymap;
 	ListBase timekeymap;
-	
+	/* keymaps have to be NULLed in readfile.c */
 	
 } wmWindowManager;
 
diff --git a/source/blender/windowmanager/intern/wm_event_system.c b/source/blender/windowmanager/intern/wm_event_system.c
index 061a784ea91..e4c4406b8ae 100644
--- a/source/blender/windowmanager/intern/wm_event_system.c
+++ b/source/blender/windowmanager/intern/wm_event_system.c
@@ -252,6 +252,7 @@ void wm_draw_update(bContext *C)
 			if(win->screen->do_draw)
 				ED_screen_draw(win);
 
+			/* regions are menus here */
 			for(ar=win->screen->regionbase.first; ar; ar= ar->next) {
 				C->region= ar;
 				
@@ -519,6 +520,7 @@ void wm_event_do_handlers(bContext *C)
 			
 			action= wm_handlers_do(C, event, &win->handlers);
 			
+			/* modal menus in Blender use (own) regions linked to screen */
 			if(wm_event_always_pass(event) || action==WM_HANDLER_CONTINUE) {
 				ARegion *ar;