It sounds like an issue like this:
http://gamedev.stackexchange.com/questi ... wall-tiles
The tilemap object merges the collision polygons of tiles with the default box collision. The result is the right wall is probably one full rectangle so there is nothing to snag on. Usually at least, it mainly depends on which tiles are merged.
Custom polygon tiles can't be merged together so that's probably why it still trips on corners.
The link above talks about solutions that probably are mostly usable from the engine level. As a user we could post it to the bugs forum and see if there's any fix that could be done.
Other ideas could be to use a second tilemap with half sized tiles. That way you can still get that tile merging and avoid corners to snag on. There are probably some other similar ideas. If it becomes too tedious you can automate it with events. If that gets too slow then you could just run the events once after you tweak your level and copy th tilemap's json to load when you actually want to run your game.