Created attachment 148355 [details]
Report generated from inside Krita 5.0.5

Stamp brushes have several problems -
1) they won't reliably use an image stack, eg where there are 5 layers, all visible & different, I now
only get the top image, whether there is a selection defined or not. Versions 4.X works fine.
2) the scratchpad in the brush editor uses the number of pixels as the source image for the stamp you are making.
This makes the scratchpad unusable, (this didn't happen in versions 4.X), so you can't preview the stamp you've made.
3) the icon for a new stamp also uses the same rez from the stamp source images as in 2) above, usually very small, & so
the icon becomes extremely blurred.
4) there is STILL the same name confusion in the paintoppresets folder that has always been there, & now
this extends to the image stack loaded for a stamp being made. It has something to do with the ")" symbol, present
in some of the names of the brushes Krita comes with. For now I can rename everything I use starting with alpha characters only, but you really need to get rid of the ")" in the names, as Python has multiple uses for that syntax symbol, & it's a problem, even in strings with quotes in the code.

The only way I can build a stamp reliably is either to make it in version 4.X & import it
or hide everything in the paintoppresets folder (rename the folder, & "fake" the bare minimum) then make one
stamp at a time. I can bring back the other brushes etc later.

I can't send you a file to show you what's going on, because it's all happening in the brush settings window.
The same problems are happening on two different machines, here's the report from one of the machines -