Bug in Control Panel or what?

Under Admin -> General Configuration, First preference: “is system on?”, If I set it to “no” and hit submit, the system goes offline but the radio button switches to “yes”. Same thing happens if I set it to “yes”, the system goes on (I can see the setting in the config.php file), but the radio buttons switches to “no” . Am I missing something? Any idea? Thanks in advance,

Guido