Whenever you click down on a spell it doesn't cast until you release which is fine, however if you click on it and move the mouse off the icon it still casts it once you release it. It should only cast on mouse up when the mouse is over the spell. Really annoying when the battle changes before you have time to release the mouse and don't want to waste the spell.

I can vouch for this. I rarely use mouseclicks for buttons, but on the occasion that I do, it is very annoying to discover the clicks are triggered onClick and not onRelease. This is standard functionality in just about every application known to man.