Hero AI question

I haven't found this discussed anywhere (and I'm not sure I'm not seeing things :P) but I'll ask anyway. I was farming illusionary team in zaishen for an easy&fast 2k balth faction and I was using 2 ele nukers, 1 monk, while I brought frozen soil. I was putting on frozen soil and let the heroes do the rest (wasn't even attacking, just standing there - yes I was lazy :P). However I had the impression, that when the enemy team stopped to cast Healing Signet (they took more or less the same dmg, so were synced) my heroes would stop attacking and resumed only when foes restarted attacking. I find it a very strange behavior, so am I just imaging things or is it true?
(sorry for my bad english)

AI stuff. I never noticed the attack bit but I know that heroes are much more keen on using offensive stuff when the player attacks aswell and that if you have same two skills on two heroes and on one it is specced higher than on the other the lower specced hero will give a priotiry to the higher specced one.