I only found one bug, when I had the Mini-Gun, and the purple zombie attacks me from behind its extremely hard to kill it because you move to slow to turn around and kill it
:D. It's not the only one! Try to hit mode 1, mode 3, blue, red, and even the "game over" off ;)
(AKA, they ALL can get hit just right to fall off the screen :P)
I think that you should be able to add hotkeys for dtrumming because when you try to do a song somtimes your not fast enough to hit all the notes,With hotkeys it would be much easier to play faster songs that require you to move up and down quickly
Check your Flash storage: Right click in game, Settings