This only happens when I have Krita open on my secondary monitor, and only with the current nightly appimage. The 4.2.8 appimage works fine on either monitor.


STEPS TO REPRODUCE
1. Put Krita on your secondary monitor not in full screen mode
2. Create or open an image
3. Hit "tab" to switch to canvas only mode. Works fine!
4. Hit "tab" to switch out of canvas only mode.

OBSERVED RESULT

Krita now displays in full screen mode. Though when you open the "View" window, you see that Krita thinks it's not full screen (no ckeckmark next to Full Screen Mode). So when you click "Full Screen Mode", nothing seems to happen except that Krita sets the checkmark. Now you can click "Full Screen Mode" again to switch back to normal mode, and everything is fine again.

I also noticed that on the nightly, Full Screen Mode doesn't quite cover the entire secondary screen, though Canvas Mode does. Again, with 4.2.8 it works on either monitor as it should.

There's a different full screen issue in bug 416894 on Windows, which I can't reproduce, not sure if there's any relation.


Krita

 Version: 4.3.0-prealpha (git 0657457)
 Languages: en_US, en
 Hidpi: false

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: 4.9.0-9-amd64
  Pretty Productname: Debian GNU/Linux 9 (stretch)
  Product Type: debian
  Product Version: 9

OpenGL Info

  Vendor:  "Intel Open Source Technology Center"
  Renderer:  "Mesa DRI Intel(R) Kabylake GT2 "
  Version:  "3.0 Mesa 13.0.6"
  Shading language:  "1.30"
  Requested format:  QSurfaceFormat(version 3.0, options QFlags<QSurfaceFormat::FormatOption>(DeprecatedFunctions), depthBufferSize 24, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 8, stencilBufferSize 8, samples -1, swapBehavior QSurfaceFormat::DoubleBuffer, swapInterval 0, colorSpace QSurfaceFormat::DefaultColorSpace, profile  QSurfaceFormat::CompatibilityProfile)
  Current format:    QSurfaceFormat(version 3.0, options QFlags<QSurfaceFormat::FormatOption>(DeprecatedFunctions), depthBufferSize 24, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 8, stencilBufferSize 8, samples -1, swapBehavior QSurfaceFormat::DoubleBuffer, swapInterval 0, colorSpace QSurfaceFormat::DefaultColorSpace, profile  QSurfaceFormat::NoProfile)
     Version: 3.0
     Supports deprecated functions true
     is OpenGL ES: false

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

Hardware Information

  GPU Acceleration: auto
  Memory: 15796 Mb
  Number of Cores: 4
  Swap Location: /tmp

Current Settings

  Current Swap Location: /tmp
  Undo Enabled: 1
  Undo Stack Limit: 100
  Use OpenGL: 1
  Use OpenGL Texture Buffer: 1
  Use AMD Vectorization Workaround: 0
  Canvas State: OPENGL_SUCCESS
  Autosave Interval: 300
  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: 1
  Use Zip64: 0


Display Information
Number of screens: 2
	Screen: 0
		Name: eDP-1
		Depth: 24
		Scale: 1
		Resolution in pixels: 2560x1440
		Manufacturer: AU Optronics
		Model:
		Refresh Rate: 60
	Screen: 1
		Name: HDMI-1
		Depth: 24
		Scale: 1
		Resolution in pixels: 1920x1080
		Manufacturer: Eizo Nanao Corporation
		Model: EV2450-
		Refresh Rate: 60