Chance K

I can confirm I'm experiencing the same issue on Windows 10 with mobs that are occupying a small space. They phase through the walls. They cannot seem to hit the player, but I can hit the mob. Happens with zombies and skeletons at least, though I imagine it happens with all mob types. 

You're right. I made the mistake of assuming that my resource pack wouldn't impact the orientation of rails. I was wrong. I'll let the makers of the pack know that there is a problem.

EDIT: I was wrong. This does not appear to be present in 1.8.