SUMMARY

I've used "Save Copy As..." from the File menu before, and at some point during the last few months it must have stopped producing files. "Save As..." still works as intended.

STEPS TO REPRODUCE
1. Click File -> Save Copy As...
2. Select a new name for the copy of the file, one that doesn't exist yet
3. Click Save

OBSERVED RESULT
The Save dialog disappears but no new file exists. The Open dialog or Dolphin or "ls" in the terminal all show no changes in the directory where the file was supposed to be saved.

EXPECTED RESULT
There should be a new file with the name given in the Save dialog.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.105.0
Qt Version: 5.15.9 (built against 5.15.8)

ADDITIONAL INFORMATION
Also broken in KWrite, but I guess there isn't much difference anymore between Kate and KWrite at this point.

I was going to fix this as my first foray into a build on KF6/Qt6/master, but the menu action is not broken there. Only broken on my Arch package. I don't (currently) have Kate/KTextEditor built from source on KF5, so I can't say if there's a difference between that and the Arch version of Kate.