I checked the skin settings to make sure nothing had changed.
I tried different skins (been using Confluence Lite for a long time).
I tried disabling the Library and re-enabling it.
I tried deleting my old databases and profiles (after backing them up).
Nothing has helped. Anyone else having this problem? Any ideas what's causing it? For now, I'm switching back to a previous build.

edit: Went back to the previous build and everything's working again.