Lets say your in a middle of a fight, and then with for example you want to use the fireball of TB.
I select the fireball and then my target (target is in range) but the caracter just stay there not moving...
Moving him a little bit and the retrying, work.
I have not found a exact reproductive scenario, but it tend to do it right after a warp (item) and you immediatly select to use the fireball.
SOrry for my english its kinda a tricky thing.