I think it has to do with the way Town accepts mobs, as these Snow Golems are definitely not in a snow biome. Since they aren't treated like the 'livestock' mobs but are instead treated as 'utility' mobs, I believe their spawning routine is not allowed in to the Town, which is why they are instantly removed from the game on spawn.
I'm sure it would be an easy fix for Justin, Cykoh. Just wait until he gets around to it. *EDIT* I'm using the Sphax PureBD Craft 64x right now. 128x doesn't work with chrome open.
Jeremy you can put them in any biomes it's the residence thing that doesn't allow hostile mobs as in snow golem's gang rape everything
Its not the Residence system, is the fact that mobs are blocked in the Town world and Bukkit still isn't out. Once the new stuff is added to bukkit I will see if it makes sense to make a way to bypass the mob protection for these