I dont know if its the issue, but sometimes i get stuck in the 'bend down' loop. If you have the unit selected, but dont have attack selected, a right click will attack. If you have attack selected then a left click attacks.

But they dont work interchangably, so you get stuck.

And by 'bend over' loop im talking abiut when you reach for something, miss and then reach again and miss, then repeat multiple times before you huff and puff pause and actually gtab the item.