Similar issue while I'm the one casting confusion.
First confusion, attack goes into the negative.
Second cast put it back into positive AND doubled the number.
Third cast doubled that number... Needless to say I was squished like a snotling.
Example: Enemy has 40 or so attack (sadly I don't recall the enemy nor its exact attack rating). First confusion gives it -71 attack. Second confusion gives it +142 attack, third gives it +284 attack, etc.