We tried those things you suggested (single player, couldn't click on the tree, leave/return to homestead). Triggering combat is no good, although the weapons drawn triggers the warning conversation, but nothing more. We'll generate a report and e-mail it to you.
We actually got past by loading a previous save before we went to Homestead after the events prior. Hopefully the save info will tell you guys what went wrong in case someone else has the problem.
EDIT: Killing Zigzax is genius. My brother is now withering under Arhu's onslaught. Apparently he didn't move Zigzax far enough away. I found it quite hilarious. Thanks.
