Possible GTK/GDK bug with touchscreen and GTKPaned

Hello everyone,

I wondered if I could get some advice about a problem I’ve been trying to debug.
I have a glade GTK layout (layout.glade, attached) for a touchscreen app (app.py, attached). It has a GtkPaned split box, with a GtkBox on the left and a tabbed GtkNotebook on the right.
I have an issue where the buttons (particularly the notebook tabs but others too) are unresponsive to touches, despite touches being registered by GTK/GDK as shown by GDK_DEBUG. This doesn’t happen 100% of the time but is easy to reproduce after a couple of slides and presses. It happens after you slide the GtkPaned split view to adjust the respective pane sizes, then go to press a button.

My working theory is perhaps a bug with GTK/GDK, it seems like the app is occasionally still on a sliding “mode” when a button is pressed. I say this because the GtkPaned slides when you move your finger after pressing down on a button. I am sure to fully let go of the touchscreen inbetween presses, and I do not put my finger too close to the split bar.

I’d like to get to the bottom of this if possible and perhaps submit a patch, but I wondered if I could get any advice first on where to look or the best way to debug.
Strangely we didn’t have this problem with the previous version of Debian.

Sorry to be a support leech, but it is at least an open source project : GitHub - devtank-ltd/devtank-dtlib: Devtank's Production Tester Framework

All files can be found here:
https://drive.google.com/drive/folders/18PEgJSM6ZWNGpe83_TaOfGeh94zfWFl4?usp=sharing

Could anybody give me any pointers?
Thanks.