It's been broken for a while. The "keyboard helper" doesn't set the key repeat delay and interval, so we never schedule the key repeat timer.
Things have been working well enough and no-one noticed!
Fixed in r17649.
Not sure if we should bother backporting this, added to wiki/Versions/PendingFixes
GTK triggers key repeat events anyway, so we send key events that have the same effect as the "key-repeat" packets.
r17650 + r17651 just rips it all out.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1724