In both creative and survival I have had iron golems spawning half in blocks of glass and unable to move. This happens in my iron golem farm, and always seems to happen on the west side (not sure if that is a coincidence or not, but it has been numerous times). The occurrences are random, sometimes going days without it happening, other times multiple times in a row.

When spawning in the glass, the golem is unharmed, but unable to move other that rotating to face other directions. In addition, when attacked (by me to clear them out) they are seemingly unable to attack back.

Sorry about the use of a texture pack in the attached pictures, should it happen again before this issue is resolved I will upload new pictures with the vanilla texture