Kick hotkeys on release, not press

I use keymap_options=grp:lctrl_lshift_toggle for layout switching. But Weston handle key bindings on press and not release, so I can't use ctrl-shift-tab in Firefox or ctrl-shift-c for copy terminal output.

The Xorg has the same bug, described here: https://bugzilla.freedesktop.org/show_bug.cgi?id=865