Hi, thanks for the report! I've moved your topic to the Battle System Bugs subforum so the issue can be looked into later.
You may also want to make a post on the "PvP Rules and Revamp of Bugged Moves / Abilities / Items not to be Used in PvP"[/url] thread, so that Mega Drain can be added to the list of known moves that are bugged.
Okay, thank you so much :)
I will make a post on the other section too then.