When this flag is set on a MetaKeyBinding, mutter will know that
the keybinding has an associated reverse keybinding triggered with
the shift modifier. However, an undesirable side-effect is that
gnome-control-center keyboard panel does not know that this 'shift'
is reserved for these reverse keybindings and cannot detect
conflicting bindings in this case.
This 'reverse' logic can now be handled at a higher level (in gcc keyboard
panel) so this commit removes it from gnome-shell so that they do not
conflict.
https://bugzilla.gnome.org/show_bug.cgi?id=732296
e8fa2b6417