It realistically should actually be smaller but since I'm using my game engine there's overhead involved that would of been too time consuming to remove.
If your landing on the ground and it's crushing you after moving it's a bug. Otherwise your getting crushed by the block pushing you into the stationary block the physics doesn't give much room for leeway so if your in even a little that's it.
*Edit*
I actually think I see what your referring too now. Yeah it's a bug / the physics being overly tight since the place your trying to fall down between is exactly the players width when the one block updates it pushes you into the other(doesn't check that the other block has moved (*Bug*))