I recognize that this isn't a problem that will normally occur, because I was running it with my level 85 mage, and with a standard 5-man group the problem propaply won't happen.
Anyways. I started the battle with the guy where you need to pick up a shield to protect yourself from the archers, otherwise you'd get knocked back. Most likely you need to do this even as a level 85-90, cus you'll still get knocked back. But before I picked up the shield, I got close enough to put living bomb (a DoT) on the boss. But when I reached his dead body, my character wouldn't drop the shield.
Thereby I was forced to walk (very, very, veeery slowly because of carrying the shield) out of the instance.
I therefore suggest that you add a mechanic where you have the opportunity to drop the shield whenever you want ;)
Sorry for the long story :P
Not only did you cut the nuts off of a previously very enjoyable set of instances in your blind race to LFD ALL the Things, you also created a mini-boss that is more awkward than any of the full bosses in the instance, AND created a "bug" like this and then ignore the ever-loving crap out of it for two years.
You either dot them and run up when they're too dead to knock back, or wait until they aggro onto you and the shield drops before killing them. It's not particularly complex nor hard to figure out. I'd rather see issues in current content sorted than dev time wasted on easily avoidable issues in overlevelled old content; fixing this could cost us a raid tier.