shop undo bug

i posted about this a while ago but i didnt understand bug but now i do so its easy to replicate just get in a custom game pick any champ dont buy anything go take dmg from the tower not enough to kill you then back buy boots or pots not a dorans cause it gives you hp then press undo and you will see your hp and sometimes mana drop to where it was when you bought the item it is the most annoying bug in the entire game to me cause i hate having to wait the extra time to heal