Bug with barricade and snare

[Thaecrasis]

I just recently noticed that if you place a barricade on top of a snare, they will stack, and if you attack the square, it does damage only to the barricade. Once the barricade is destroyed the snare is revealed again.

It seems like this could simply be a game mechanic, but I thought I'd note it here, just in case.
Log attached.

Edit: After destroying the snare, it becomes an impassable tile.
Image: http://i.imgur.com/AQ81y3N.png

Note: the tile is passable by fliers.