I was playing the Java Snapshot with my brother and we were killing each other, and we noticed both of our weapons were unable to inflict fire damage from fire aspect 2. I have keep inventory, normal mode, and instant respawn on. The armor I was wearing is all thorns 3, prot 4, unbreaking 3, and mending.

UPDATE: I apparently set fire damage to false and had forgotten, this is not a bug, and I'm not sure how to delete this bug report.