Created attachment 156683 [details]
Tiled-Gwenview

SUMMARY
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When I tried out the new tiling in Plasma 5.27, I noticed that some (not all) apps get completely distorted titlebar graphics, sometimes during a tiling, sometimes after coming out of the tiling mode. This was noticed under Wayland.
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STEPS TO REPRODUCE + OBSERVED RESULT
1. Log in into Wayland session
2. Have third party aurorae theme, like WhiteSur-dark
3. Apply new tiling (shift+drag window), resize the titled windows, then drag the window out of tiling. Some apps (didn't find a rule yet), like for example Gwenview, get completely distorted titlebar graphics - see the attached screenshot.




EXPECTED RESULT

Third party titlebars should maintain properly updated graphics during and after tiling.


SOFTWARE/OS VERSIONS
Operating System: Manjaro Linux 
KDE Plasma Version: 5.27.1
KDE Frameworks Version: 5.103.0
Qt Version: 5.15.8
Kernel Version: 6.1.13-1-MANJARO (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i7-6700HQ CPU @ 2.60GHz
Memory: 7.6 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 530
Manufacturer: Alienware
Product Name: Alienware 17 R3
System Version: 1.13.1

ADDITIONAL INFORMATION

I am still finding a rule, but so far it looks like a random occurrence. Once I saw it with Thunderbird, then I couldn't repeat it. Then I saw it under Dolphin, then I couldn't repeat it. Now, I caught this bug on Gwenview and made the screenshot.
Sometimes the problem is visible during a tiling, and then it's fixed when the app is out of tiling mode. Sometimes the bug stays.
Weirdly, when the graphics returns to normal out of tiling, when the app is tiled, the same visual bug appears right away, as if it was remembered.
During the writing this bug description, I couldn't repeat it on Dolphin, but then I tried again, and the bug came again and is repeatable. When the window is widened above half of the screen, the titlebar is widened horizontally. When the window is below the half of the screen, the titlebar is shortened beyond the windows width and the titlebar graphics is distorted.
I haven't tested it under X11, so I don't know if the bug happens there as well, but I suspect it may be a Wayland thing.