Created attachment 124343 [details]
example presets and patterns to show this bug

SUMMARY
This problem happens in krita 4.2.7.1 and 4.2.8 appimages and the latest Dec 06 Windows .zip build g818c841b0b
It does not happen in 4.2.6.

It happens with quite a few of the brush presets and the common factor (the one that I've noticed) is that Pattern is enabled and uses a .pat pattern file.

I attach a zipped collection that illustrates the problem.

Ahab-Speed_Skin-Reptil_Copy.kpp is an unaltered copy of the Speedpaint-Skin-Reptil brush preset.
Ahab-PNG-Speed_Skin-Reptil_Copy is that preset changed to use a .png pattern instead of the .pat cazu-reptile pattern.
cazu-reptile.pat is the normally used pattern file.
Ahab-PNG-cazu-reptile.pat is after I converted it to a .png file.

STEPS TO REPRODUCE
If you use Ahab-Speed_Skin-Reptil_Copy then it doesn't work except in krita 4.2.6.

If you open the Brush Editor and change any parameter or control then change it back to the original setting, the brush preset will work. If you then open the Brush Editor and reload the brush preset, it no longer works.

Ahab-PNG-Speed_Skin-Reptil_Copy does not have this problem, the only difference being that it uses a .png version of the original .pat pattern file.

OBSERVED RESULT
As noted above

EXPECTED RESULT
It should work, as it does in 4.2.6

SOFTWARE/OS VERSIONS
Krita

 Version: 4.2.8
 Languages: en_GB, en
 Hidpi: true

Qt

  Version (compiled): 5.12.5
  Version (loaded): 5.12.5

OS Information

  Build ABI: x86_64-little_endian-lp64
  Build CPU: x86_64
  CPU: x86_64
  Kernel Type: linux
  Kernel Version: 4.19.0-6-amd64
  Pretty Productname: Debian GNU/Linux 10 (buster)
  Product Type: debian
  Product Version: 10

OpenGL Info
 
  Vendor:  "NVIDIA Corporation" 
  Renderer:  "GeForce GTX 750 Ti/PCIe/SSE2" 
  Version:  "4.6.0 NVIDIA 418.74" 
  Shading language:  "4.60 NVIDIA" 
  Requested format:  QSurfaceFormat(version 2.0, options QFlags<QSurfaceFormat::FormatOption>(), depthBufferSize -1, redBufferSize -1, greenBufferSize -1, blueBufferSize -1, alphaBufferSize -1, stencilBufferSize -1, samples -1, swapBehavior QSurfaceFormat::DefaultSwapBehavior, swapInterval 1, colorSpace QSurfaceFormat::DefaultColorSpace, profile  QSurfaceFormat::NoProfile) 
  Current format:    QSurfaceFormat(version 4.6, options QFlags<QSurfaceFormat::FormatOption>(DeprecatedFunctions), depthBufferSize 24, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 0, stencilBufferSize 0, samples -1, swapBehavior QSurfaceFormat::DefaultSwapBehavior, swapInterval 1, colorSpace QSurfaceFormat::DefaultColorSpace, profile  QSurfaceFormat::CompatibilityProfile) 
     Version: 4.6
     Supports deprecated functions true 
     is OpenGL ES: false 

QPA OpenGL Detection Info 
  supportsDesktopGL: true 
  supportsOpenGLES: true 
  isQtPreferOpenGLES: false 

Hardware Information

  GPU Acceleration: none
  Memory: 16039 Mb
  Number of Cores: 8
  Swap Location: /tmp

Current Settings

	Current Swap Location: /tmp
	Undo Enabled: 1
	Undo Stack Limit: 18
	Use OpenGL: 0
	Use OpenGL Texture Buffer: 1
	Use AMD Vectorization Workaround: 0
	Canvas State: OPENGL_SUCCESS
	Autosave Interval: 360
	Use Backup Files: 1
	Number of Backups Kept: 1
	Backup File Suffix: ~
	Backup Location: Same Folder as the File
	Use Win8 Pointer Input: 0
	Use RightMiddleTabletButton Workaround: 0
	Levels of Detail Enabled: 0
	Use Zip64: 0


ADDITIONAL INFORMATION