I don't know how this happens because it feels random. If I mix mouse and pen input on GTK applications they can completely break and reject any input. The first thing I notice is a offset between mouse click and cursor hover input on drop down menus. If I continue to click on things on the GTK window using pen and mouse they completely reject any input. tested on Xournal++ and mypaint Operating System: openSUSE Tumbleweed 20210524 KDE Plasma Version: 5.21.5 KDE Frameworks Version: 5.82.0 Qt Version: 5.15.2 Kernel Version: 5.12.4-1-default OS Type: 64-bit Graphics Platform: Wayland Processors: 16 × AMD Ryzen 7 3700X 8-Core Processor Memory: 15.6 GiB of RAM Graphics Processor: AMD Radeon RX 5700
This would either be a bug in GTK itself, or in the relevant drivers (libinput and/or wacom; depends on which drivers you have active. I suspect GTK itself. Regardless, please report it upstream first https://gitlab.gnome.org/GNOME/gtk/-/issues/. If they insist it's not their fault, we can re-investigate this here. Thanks!