"Send job completion message to members of this group" always resets to "Admin"

Hi,
I'd be thankful if someone could help with this:
Under the job preferences tab there is the setting under "Send Job Completion
message to members of this group:" with a pop-up-list.
Whenever I set this to another group and click the submit-button the setting
resets itself immediately to "Admin".
I have created a new group with the full permission list and tried to select
this one, I have switched my German language setting to English, I have
deactivated the wysiwyg-editor and the syntax-highliter under my user
preferences, I have switched the theme from OneEleven to NCleanGrey – nothing
helps.

The installed modules are:


    CMSMailer: [b]5.2.1[/b]
    FileManager: [b]1.4.2[/b]
    MenuManager: [b]1.8.5[/b]
    ModuleManager: [b]1.5.5[/b]
    News: [b]2.12.10[/b]
    Printing: [b]1.1.2[/b]
    Search: [b]1.7.7[/b]
    ThemeManager: [b]1.1.7[/b]
    TinyMCE: [b]2.9.12[/b]
    FileBackup: [b]0.5[/b]
    MysqlDump: [b]1.2.4[/b]
    Gallery: [b]1.6[/b]
    CGExtensions: [b]1.31.4[/b]
    FrontEndUsers: [b]1.21.2[/b]
    CustomContent: [b]1.8.3[/b]
    TemplateExternalizer: [b]2.0.8[/b]
    NMS: [b]2.7[/b]
    CMSPrinting: [b]1.0.3[/b]
    MicroTiny: [b]1.2.4[/b]
    CGJobMgr: [b]1.2.11[/b]
    AceEditor: [b]0.2.5[/b]

Thanks for helping

Reinhard