When choosing the targeting option the towers will attack the first target they see and keep attacking that target until it dies or goes out of range before choosing the next target based on the priority chosen and repeat the idea of not changing targets until current one dead or out of range. This defeats the point of the targeting options if the towers don't recheck their priority target after every shot. I first started to notice this when using the poison tower with random targeting and it wouldn't change targets after each shot, which made the poison tower completely worthless. It wasn't like this in the original infinitode, so I assume it is a bug.