Removing own user group membership, sets user with no module access, and then you are locked out. You then can then only modify the webmin.acl to regain the module rights back.
It should at least keep the previous group module access rights.
To mention that the user has sudo rights.
Did the user previously inherit all module permissions from the group? If so, this is kind of expected .. although arguably should trigger a warning if you do it for the currently logged in user.
The user had access rights to all modules previously, because was the first user with sudo rights to login to webmin.
I tried this scenario also.
User with full module access rights (webmin.acl reflects that also). Added to a group with all module access. Set the group membership to none to the user. The user looses all module access rights (webmin.acl user looses access to web visible modules)
Last edit: BogdanV 2014-06-27
Ok, I see the bug now that causes the check to prevent this to stop working - it will be fixed in the next release of Webmin.