I noticed this bug on paradise meltdown where the minions get stuck just past the first grinder on their way to the second one. It may have happened while I using Atticus’ ultimate and bouncing a bunch of enemy minions around them. Anyway, it made a traffic jam. You can see in the imgur link here: http://imgur.com/a/oGUQa They just jostled back and forth. I tried buying an elite bot to see if he would break them up but no avail, nor did the enemy wading in occasionally and killing some of them.
I’ve seen this happen on Overgrowth as well, minions get knocked off course and fail to re-renter the battle. It’s rare, but it happens.