On my windows machine, there seemed to be a missing reference to the image data when a stamp was being created. The image was being set near the beginning of the application, but the reference turns into null by the time the stamp tip needs to use it.
This fix just sets the image data when the brush editor appears. It appears to make the stamp brush tip work
I checked my Ubuntu system later and the current stamp problem also happens on that. for some reason I thought it was only on Windows, but I was mistaken.
uhh. I can't find the "Krita" repository when assigning it in the ticket, so I just assigned it to the dithering extension.