Created attachment 146965 [details]
bundle of buggy brushes

SUMMARY
Changing any MyPaint brush engine parameters changes the brush destructively, i.e. even if the settings are put back to what they were. This isn't a disaster because you can just go to another brush and back to revert them, but it means you can't change the brush settings without ruining the brush.

STEPS TO REPRODUCE
1.  Download and import the attached brush pack
2.  Go to brush editor and select one, I recommend the flat brush - notice how it looks in the preview window
3.  Try painting with it a bit (it's a nice brush, feels very physical!)
4. change some brush param, them change it back: eg go General > Basic > click Eraser checkbox, then click it again so it is once again false
5. Notice how in this process the preview window has changed dramatically, and did not change back
6. Try painting with it. In my case, the brush felt less opaque/wet and did not blend correctly.

OBSERVED RESULT
Brush does not change back to original look + feel when settings reverted.

EXPECTED RESULT
Settings reverting should leave the brush as it was.

ADDITIONAL COMMENTS:
Many of the settings for these brushes seem glitchy (the curves are clearly not well formed). Is it possible that these brushes were made with a version of mypaint not supported in Krita yet? Please let me know what you think. They are excellent brushes for painting and it would be a shame if I couldn't work with them/edit them.

SOFTWARE/OS VERSIONS
Windows:  10
Qt Version: 5.12.12

ADDITIONAL INFORMATION
Krita
 Version: 5.0.2
 Languages: en_US, en
 Hidpi: true

Qt

  Version (compiled): 5.12.12
  Version (loaded): 5.12.12

OS Information

  Build ABI: x86_64-little_endian-llp64
  Build CPU: x86_64
  CPU: x86_64
  Kernel Type: winnt
  Kernel Version: 10.0.19044
  Pretty Productname: Windows 10 (10.0)
  Product Type: windows
  Product Version: 10