After reading how the exp and gold actually work, I started to "tag" creeps, (hit them once, then switch to next, hit it once, then switch to next.), when I discovered this bug (mostly playing oak, but seems to be on other demigods also):

If you chance the target you are attacking, the attack animation chances immediatelly to attack the next target, but ___the first attack does no damage___. Only the second attack on the same target deals damage.

It is possible to get the first attack to deal damage, but you need to time it perfectly: JUST when you land a blow to a creep, at that same microsecond you need to chance the target of your next hit. If you chance your target even a fraction of a second late, the demigod will do the attack animation, but the blow will deal no damage, and you just missed the time needed to attack once.

Highly annoying bug, making it almost impossible to "tag" creeps with demigods that have no AOE damage.