No, on looking closer its nothing to do with keybindings (AFAICT) its the implementation of `keygrab()`.
That should be implemented by adding a signal handler for keystrokes _before_ Geanys on the normal GTK keystroke signals "key-press-event" and "key-release-event" (IIRC). That will still allow it to block keystrokes from Geany (bad form, but possibly necessary) but not have to dive to the low level of event filters on widgets and will deliver a portable `GdkEventKey`, not the non-portable underlying OS structure that needs X11 or (in the #else) `windows.h` and doesn't handle Wayland.