There has been a bug the last couple patches where heros will swing or shoot and hit targets other than the target you right click. For example Oak will swing his weapon and hit whatever is closest to him instead of the target you right click. This bug is particularly bad with QoT.
I only play generals and TB and it doesn't happen to me when I play TB so I have a feeling it involves the control of pets with units. Hopefully this can be fixed because right now I can't see any reason to play QoT with her wildly shooting all sorts of shit other than what I want her to hit.
Oh, it also happens when a target is fleeing from you... I.E. you're QoT and a player is running away and they aren't faster than you so you keep firing shots, but if creeps are between you and them your hero will priority the creeps over the target you specified.
I wish I could be more specific about the bug, but that's about it...
I noticed the creep AI is also messed up too, sometimes I have my minions and my hero attack the same target and the minions will just attack w/ is nearest them so i have to manually control both sets which isn't really a problem, but I'm pretty sure it's not intended to function so randomly.