Happened s to me a LOT. Mostly after one of my melee units swings. I can reduce the chance of it happening by waiting longer between clicks (like Heavenfall suggests above). Doesn't seem to matter if I click too fast when my archers are shooting, though. So I think it is timing-related in some part of the code path that is separate for melee and bow attacks.
And I'd vote for fixing too, but I think it needed to be done before most of the team moved over to FE. If Brad is the only one still working on WOM, I think we are SOL because this is probably outside his area of competence -- they would have to pull a coder off of FE for a slow and frustrating debugging ordeal.