mobs spawning in blocks and not coming out

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here

What actually happened was...:
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...i expected the mobs to stand on the blocks
3. ...some mobs like creepers and villagers spawned inside the blocks and when i tried to get them out they stayed in there
this was in the version 1.7.1 pre release