[TYPO3] denying editing og a FE plugin does not work

[micho]

Hi, I want to deny users editing a special Frontend-Plugins type.


therefor I configured under Backend-Usergrour Rights
Explicitly allow/deny: Frontend-Plugin to deny is checked.

If an user of this group (without any other rights except the ons from 
his group) tries to edit this Frontend-Plugin it works (but should not!).

In the editing dialog under plugin(Typ) stands: "aktueller Wert ist 
nicht erlaubt"  (actual value denied)

What´s wrong with that.