You need to validate and fix your code (you have major errors that can really mess up display). Also, check your theme’s header.php links, they have missing double quotes.
Thanks, Iridiax. I’ve fixed a few of the errors, though I think getting all of them is beyond my skill level at the moment. Trying to fix others has led to further display problems, which I’m sure is my fault for hacking together a theme whose workings I don’t fully understand.
I’ll leave this unresolved through the morning in case anyone spots the specific error that might cause the sidebar problem. If no one does, I’ll assume I’m stuck with this until I am able to do a more thorough debugging.
Fix the div errors first, these ones usually cause the type of display issues you describe.
OK, thanks, I will work on those and hopefully get this fixed. I appreciate the tips.