When I go to Settings -> Menu Editor -> Settings and click on the save settings button, it takes me to the login screen (even though I was already logged in without time-out). After logging in again, it takes me to a plain version of the settings page again (i.e. without the admin bar, admin menu etc) and the changed options have not been saved.
If I then change the options again and click on the save settings button, the settings *are* saved and I'm taken back to a normal version of the settings page.
Tried several times with same result, though I have to admit this is on a WP 3.4.2 install which I'm in the process of upgrading.