wacom drawing tablet configuration doesn't let you assign modifier keys to buttons

[mjau]

Wacom drawing tablets has a set of buttons that can be configured to send keypresses. It's useful to assign pure modifier keys to these buttons, to work as modifiers for pen input – for example, in GIMP, holding ctrl lets you pick colors from an image without having to explicitly switch from the brush tool to the color picker tool (and back again).

Ubuntu's wacom configurator doesn't let you do this though. On the button remapping screen, modifier keys simply aren't recognized as input unless a "regular" key is pressed as well. I can assign "ctrl + z" to a button, but not "ctrl" by itself.

$ lsb_release -rd
Description: Ubuntu 13.10
Release: 13.10

$ apt-cache policy gnome-control-center
gnome-control-center:
  Installert: 1:3.6.3-0ubuntu45.2
  Kandidat: 1:3.6.3-0ubuntu45.2
  Versjonstabell:
 *** 1:3.6.3-0ubuntu45.2 0
        500 http://no.archive.ubuntu.com/ubuntu/ saucy-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     1:3.6.3-0ubuntu44 0
        500 http://no.archive.ubuntu.com/ubuntu/ saucy/main amd64 Packages

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.