SUMMARY
I noticed clipboard problems in some circumstances. Tested on Firefox and Chromium with slightly different symptoms.

STEPS TO REPRODUCE
1. Open Firefox
2. Type something in the address bar
3. Ctrl+A, Ctrl+C
4. Ctrl+T (to open a new tab)
5. Ctrl+V

OBSERVED RESULT
Nothing gets pasted

EXPECTED RESULT
The copied content should be pasted

- This also happens in this textbox for entering the bug report. If I copy content and try to paste it, nothing happens. If I copy it a second time, it works.

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On Chromium the clipboard seems to be off by one - the previous copied content gets pasted, not the currently copied content:

1. Open Chromium
2. Type "test1" in the address bar
3. 3. Ctrl+A, Ctrl+C
4. Ctrl+T (to open a new tab)
2. Type "test1" in the address bar
3. 3. Ctrl+A, Ctrl+C
4. Ctrl+T (to open a new tab)
5. Ctrl+V

Result: "test1" gets pasted, not the more recent "test2". - Currently I cannot reproduce that and instead some other even more weird behavior happens on Chromium.

SOFTWARE/OS VERSIONS
Operating System: Manjaro Linux
KDE Plasma Version: 5.20.0
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.1
Kernel Version: 5.8.14-1-MANJARO
OS Type: 64-bit
Processors: 4 × Intel® Xeon® CPU E3-1225 v3 @ 3.20GHz
Memory: 11.6 GiB of RAM
Graphics Processor: Mesa DRI Intel® HD Graphics P4600/P4700

ADDITIONAL INFORMATION
Happening on Wayland.

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