I was testing a command machine I had made in the new snapshot to see how it effected it's performance, and apart from color signs, tellraw, title or anything else with json not working properly, I thought I had not come across any major issues. Until I stumbled upon this. Spawn eggs with NBT data do not function right. Though having the correct damage value, they appear blank, therefor preventing them from spawning entities. This would ruin my MCE sires and since I haven't seen anyone else report this bug I thought I'd give it a shot. I believe this most likely effects other fields of the "display" NBT argument, but I cannot be sure.