i have gloom (idk if only this pokemon have this bug maybe more pokemon were use drain have this) and i use mega drain,i recieve the heal and after that the i take damage (like 2-3 damage) and then the leftover heals it (i have leftover item equiped on gloom) what the..? :D

2-3 what? HP? If you only lost a little HP then of course the leftovers are going to heal it afterwards. If it is 2-3 times the damage that mega drain did to the other Pokemon and all that HP was healed instantly, then yeah it would be a problem.

i mega drain and i heal after the mega drain enemy dont even attack and i lose 2-3 hp and then leftover work and heal it..its like i dont have leftover -.-