Running the client in fullscreen with system keys enabled results in the client locking up, and using 100% CPU, if the client uses Xorg 1.20 or newer.
Reported upstream here:
Complained to Xorg folks here:
Upstream workaround here:
Works well now. Tested on Fedora Rawhide with GNOME desktop (Xorg 1.20.1). I could provoke the bug with 4.9.0 both with Xorg and Xwayland. After an upgrade to trunk the client worked well in both environments.