linuxmint/Cinnamon — pull request #1290 by mtwebster (2012-10-19 23:14:09+00:00)
Title: Change modifier type for keybindings page.

Turns out, MODIFIER_TAP only seems to exist for Ubuntu (I found it in
devhelp), but not in GTK proper, so invalid in pure GTK environments.

This prevents the ability to set a single modifier key as a keybinding,
but all other key combinations are possible as normal.