Created attachment 178131 [details]
image of the behaviour

SUMMARY


STEPS TO REPRODUCE
1. Select an area with the selection tool.
2. With a color smudge engine brush, do a brushstroke that overextends the selected area. (Also works with the canvas border.)

OBSERVED RESULT
If the center of the brush cursor goes outside the selected area, it will sample pixels outside the selected area, if there isnt any pixels to sample, it will erase the previous drawn pixels.

EXPECTED RESULT
The brush shouldnt sample anything outside the area or canvas border.

ADDITIONAL INFORMATION
Recreated on both Windows 10/11 and Android with exactly the same results, I created a thread in Krita Forums and people have agreed this is a known behaviour of color smudge brushes. Credit to user ¨YRH¨ for creating the attached image.