I have the same issue and Comment #18 has the solution:
Whereas the "Linux console" keyboard mapping correctly maps Ctrl-Space to outputing \x00, the "Default (XFree 4)" keyboard mapping incorrectly maps it to no output.
I believe this is the bug, and the "Default (XFree 4)" keyboard mapping ought to map Ctrl-Space to outputing \x00 like the "Linux console" keyboard mapping does.
I have the same issue and Comment #18 has the solution:
Whereas the "Linux console" keyboard mapping correctly maps Ctrl-Space to outputing \x00, the "Default (XFree 4)" keyboard mapping incorrectly maps it to no output.
I believe this is the bug, and the "Default (XFree 4)" keyboard mapping ought to map Ctrl-Space to outputing \x00 like the "Linux console" keyboard mapping does.