I am having your exact same problems. I happen to use themes based on the classic theme. Quite frankly, the 'classic' theme they made for RC2
is currently of poor quality. It's a poor conversion. No attention to detail was paid. I've found many things that are broken from what it was in RC1.
That's just some of many differences. The linktree spaces differently, the post page is mangled, the search results page is missing borders, the personal message center is broken, problems on the moderator reports pages, profile pages are mangled etc. It's a mess.
Just compare the classic theme in RC1 with the classic theme in RC2 and you'll see so many issues you won't remember them all! Hell, it's so bad using the RC1 version as-is in RC2 actually looks BETTER in several instances.
I'm very disappointed. Especially to see such drastic regressional changes after a supposed candidate for release was released. If you ask me, the classic theme has reached the end of the road. The devs don't care about it anymore. I doubt anyone is going to make a properly working version. I started fixing some of the issues myself and then decided it was probably more effort than it's worth because there's so many and I'm not intimately aware of all the CSS and structural changes made that the theme creators are.
The classic theme relies on "compat.css" which is even clearly stated in the file it's an attempt at best. They were so obsessed with pushing Curve in there after a release canddiate was already out, nothing else mattered.