Bug: sometimes units when specified to fire at a certain unit, will continue trying to do so even after it's destroyed. probably lost a ranked match because of this http://pastats.com/chart?gameId=353731 Near Knarf's commander at 17:22, all the tanks fire at the wreckage.
Yes, in this case though, I never right clicked the wreckage. I right clicked the leveler. When it was destroyed, instead of the units retargeting, they fired at their previous targets wreckage and missed each time.
I've noticed this when a-moving and on patrols sometimes. They keep shooting the wreckage of things they destroy, even when there are no more enemies. Happened in PA too.