The first problem, solved for "spacebar" in r25130, is that we don't get the keyname we expect so we have to map the character to its (X11) keyname.
The second problem is that the keyname may map to a keycode that requires modifiers to be accessed. ie: "&" shows up as "7"
This is fixed in r25174 (+r25175) by adjusting the "shift" and "mode" modifiers to match the level of the matching keycode we found. This change can potentially cause problems, so it won't be backported to v3 just yet.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2574