Iron Golems cannot jump or walk up stairs/slabs

While in survival mode (but this happens in any game mode) I expected to be chased down by Iron Golems when I injured them, but I noticed that when I hurt an Iron Golem I could easily evade it by running to a higher elevation. It could not jump up to a higher elevation, and I later found that they cannot walk up stairs or onto slabs either.

Steps to Reproduce:
1. Put Iron Golem in a pit
2. Provoke it/ have it provoked in some way
3. Watch as it can't get out