Ok so not really a bug, but needs a fix.
Currently we can use the troll holes to bypass loads of creeps in rumbles grotto. Just run in, run to troll hole to lose aggro from all the creeps that chase you, run out kill one group of creeps outside the hole, kill boss... repeat! you can do this 3 times, for each of the bosses cutting out a large amount of time taken to complete the dungeon.
One group doing this were even on a live stream, discussing with eachother that no one should post it on the forum... but I think it is the right thing to do. Hence this post!
Fix could possibly be making it so you get the "You are in combat"