Avoiding defenses

I do understand that when troops are placed, they will do whatever it is they do... but I have noticed there has been a HUGE increase of troops avoiding to attack defenses. As an example, I'd like to take out a cannon, so I set a giant in and he goes to the cannon, but when placing barbarians or archers right in front of the cannon, they veer right or left with only a couple staying on the cannon. Is this in the programming to give the defense an advantage? I really am beyond frustrated with this and do not understand the inconsistency... what can be done when troops avoid attacking cannons and archer tower and mortars and wizard towers?