If the going theory is that this is caused by a dead body somehow having >0 HP, my situation must be unusual. I had just finished House of Hope, and I loaded back in to the Lower City after that without a problem. Now, between doing that and now (where I can no longer load out and back in to the lower city), I have literally not killed anything or engaged in combat at all. Now, if I go back to before I entered the House of Hope initially, I travel to Wyrm's Rock, then back to the lower city without a problem. Dunno how something in House of Hope could have broken the lower city zone. I suppose I'll just go through all of House of Hope, and see if I avoid the problem on the second try... This sucks a whole lot of ass though.
