[Typo3] Strange behaviour specialchars while logged in

[Ulf Stephan]

Hi all,
I've got a strange behavior on a Intranet.
All Sites are still utf-8 (include backend) and xhtml.
Viewing the frontend-sites everything works fine. After login at the
backend and viewing the Site in another window sometimes the special
chars like ä ü ö ß change to something diffrent.
Properties of the displayed site are always utf-8.
It appears in diffrent browsers (tested with ie and ff).

Has anybody had such a Problem?

Greeting Ulf