theme settings tabs broken when you change enabled themes

in trying to test http://drupal.org/node/132018 i noticed that when you change what themes are enabled, the menu tabs for the theme settings don't get properly rebuilt. menu_rebuild() is getting called, but list_themes() is returning stale info about what themes are enabled. i added a manual call to list_themes(true) to reset the static cache of theme info, but that's not working. :( i'm too tired to keep debugging this now, but wanted to write up my findings in case anyone else has time to figure out wtf is going on.