I have given up! I can not figure this problem out on my own!

I have a site using domains. I have two themes, Main (used on the main and most of the sub-domains) and Sub (used on one particular subdomain). When the site is using the main theme, all is well. When the site is using the sub-theme, all is well EXCEPT for the user profile page ("/user/bob" or whatever).

For some reason it always displays with the Main theme. I don't see the CSS loading in the source, and it's using the main page.tpl instead of its sub page.tpl as well. (If I edit the profile, the Edit page is displayed properly as the sub-theme.)

I have looked in my template.php (and actually, there isn't one in the sub theme) but I don't see anything that should affect only the user page.

Whatever is going on is totally non-obvious to me, and I am at a loss, at the end of my rope, and out of cliches! If you are familiar with Domains and themes, maybe you can help!

I have no idea what a reasonable bounty is -- maybe this is a super-easy fix or maybe it's a doozy; I promise I am not stingy and will pay a fair price to fix this sucker.

Thanks!