Stuck in Steaming Springs arena after defeating boss

Finished the boss battle, but can't leave the arena. Re-logging to the character screen or using a town portal just put me back in the arena again.

Looks like I can't finish the rest of this map.

Also, I noticed the arena as empty and the boss spawned in a bit slowly before the fight. I was heading back out thinking the boss must not be there when it came up out of the sand. It's possible that I was at the edge of the arena and glitched so I was in, but it thought I was out or something like that.

Bug Report ID: #1870620477

Same issue, ref #786,611,129