This might sound like the stupidest solution ever, but it's the last thing anyone would be thinking. Try playing this very map on the regular Game.exe and not the Test Play version. See what you get. Maybe it's a Ctrl thing. Other than that, I suppose a good temporary solution would be just having an event posing as an impassable space.
If you're REALLY unsure what's happening, there's a script by Rataime on .org that shows Passability Tiles on your game. I'll find it if only .org could have been more organized...I'll try though.