This is an issue observed while shift-queueing attack-move commands for all units. While holding down the shift key you are free to queue up as many attack-moves as you desire. The issue arises after releasing the shift key. For some reason, the attack-move command is still held and if you left click all of the shift-queueing you had done while shift was held will be removed. I suggest that the mouse state of issuing attack-move commands should be canceled after releasing the shift key.
I believe this to be an issue introduced after the first PUP release. If I recall correctly shift queue worked as expected before the update.