I've been using the console combat report to test the spell skill gain and there appears to be something wrong with the Pillar of Fire spell. It seems like you do not gain any skill experience if the Pillar of Fire is used to kill the monster, it only reports skill gain if the monster is wounded but not killed. This behaviour is different from similar spells such as Meteor.
A separate spell which is perhaps not bugged but at least does not quite match its description is Berserk. While active your auto-attack deals splash damage to 4 squares directly connected to the monster you are attacking, but if an auta-attack kills the monster then you deal splash damage to the 8 squares closest to your character.