The details are too long to go into in full (and I'm much too tired) but I thought I'd ask whether this kind of thing has happened to anyone.
I'm working on a WP theme on a local server, then uploading it to see it online. Basically every single file on the local version and the online version is exactly the same. I even have the same couple of dummy posts and the same links and stuff in the sidebar. Everything should look identical.
At the bottom of my template I have a div with a CSS background image which acts as the footer image. Just before that, a list of links, absolutely positioned which end up at the top of the page in the layout. The details are not important - what's important is that it worked fine on the local version, but the background image of the footer wouldn't show in the online version.
After 2 hours of near insanity, I switched the order of the two elements. Voila, now it works in both.
Forgetting about specifics, what's really worrying me is that something in the template worked perfectly on the local installation of WP, but screwed up in the online version, even though all relevant files are identical. Has anyone else ever experienced this?