/dev/dri permissions not set

/dev/dri permissions are not set correctly when logging in to an mir seat.

This is probably caused by not correctly ConsoleKit-ing the session, or something. Indeed, under this XMir session I have:
ck-list-sessions:
Session7:
 unix-user = '1000'
 realname = 'Christopher James Halse Rogers'
 seat = 'Seat1'
 session-type = ''
 active = TRUE
 x11-display = ''
 x11-display-device = ''
 display-device = '/dev/tty1'
 remote-host-name = ''
 is-local = TRUE
 on-since = '2013-01-22T04:34:11.320077Z'
 login-session-id = '4294967295'
Session9:
 unix-user = '1000'
 realname = 'Christopher James Halse Rogers'
 seat = 'Seat1'
 session-type = ''
 active = FALSE
 x11-display = ':0'
 x11-display-device = '/dev/tty7'
 display-device = ''
 remote-host-name = ''
 is-local = TRUE
 on-since = '2013-01-22T04:34:18.727880Z'
 login-session-id = '4294967295'