I can't change my time zone setting to plain GMT [View all]

European clocks switched on Sunday morning, so I needed to change my time zone from "GMT +1" to "GMT". I go to 'Account Settings', and the dropdown says "GMT +1", and I change it to "GMT 0", and then click "save all settings" just below it. The screen reloads, with the message "All settings saved" above - but it has changed back to "GMT +1", and the times displayed in forums are still GMT+1.

It will, however, allow me to change to every other time zone I've tried so far (eg GMT+2, GMT-5, USA/PT ...). It just seems to be GMT itself that it refuses to change to (whatever I'm trying to change it from).