password match error on system_usermanager causes Group membership to be reset.
I went to set the pre-shared key on my own account. In the process, a browser form filler entered my password on the first of the two password fields of the user page. When I hit save, an error came up that the passwords did not match. This error also caused my Group membership to be reset to empty (thus removing my admin and all other privileges). Next page I got gave me the dreaded message "No page assigned to this user! Click here to logout."
If this happened on a system with only one administrator, the system would be useless as far as any administration is concerned.