[TYPO3-dev] BE: usernames must not start with an exclamation mark?

[Uschi Renziehausen]

Hi folks,

I do not know whether this is a bug or not, therefore I ask here before 
reporting the issue.

In my local installation I have a few testusers with the naming scheme 
!something. If I try to login as such a user it does not work. Is this a 
bug or am I just ignorant of certain naming rules for BE usernames?

Uschi