Nobody here with the same problem?
Maybe somebody with a different linux distribution can report, if this is Fedora related or a known gnome limitation. If the last one is the case, I really feel like gnome should implement support for hotkeys and shortcuts in overview as soon as possible. If the first one is the case, I'm going to report it as bug on redhat bugzilla.
this is a really annoying thing: changing volume, taking a screenshot, adjusting brightness and all custom shortcuts can't be used in overview? how lame is that!
EDIT: It's a known bug, see https://bugzilla.gnome.org/show_bug.cgi?id=643111