Cancelling an edit doesn't forget the edit state

I set about editing the commit message of a change but made a mistake so cancelled the edit, intent on starting afresh. However, when I hit Edit again, it restored the state at the end of my prior edit, that I'd cancelled. It won't give me the pristine current version to edit from scratch - I have to manually correct the mistake I'd made, that I expected I'd be able to undo just by cancelling the edit.