Just a quick update: I upgraded my WordPress install to 2.3.1, and now the POST errors on the Dashboard are gone. However, I still get POST errors when I try to use the theme editor, or try to create new categories. *sigh*
I was having much the same issue. Turns out that when I was using Mozilla 1.7.8 (Work PC) I would get the reverting sidebar. When I used Firefox (v.2.0, Mac or PC) it would not. I am running Multizilla on Mozilla, nothing special about my Firefox install here at work.
