[winswitch] Getting UnboundLocalError when playing with xpra + docker

[hernantz]

Hi there,
I'm getting an error when trying to use xpra + docker with the 
docker-desktop image[0]:
UnboundLocalError: local variable 'xkbmap_query_struct' referenced 
before assignment (Full traceback[1])
Xpra version: xpra v0.14.8
OS: Ubuntu 12.04
Is this a known bug? May it be that my OS version is too old?
Thanks in advance.
hernantz

[0] https://github.com/rogaha/docker-desktop
[1] http://pastebin.com/RrVdyUqS