Created attachment 149052 [details]
Video reproducing the bug.

SUMMARY
The panel shadow appears wrong when the floating mode is activated.

STEPS TO REPRODUCE
1. Right click on the desktop and add a panel (doesn't matter if it is empty or not).
2. Right click on the panel to enter to edit mode.
3. Click "More options" and enable the "Floating panel".

OBSERVED RESULT
The floating panel has a shadow that isn't correctly sized (it isn't in the border of the floating panel as supposed to be).

EXPECTED RESULT
The floating panel has a proper shadow (in the borders of the panel).

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.24.90
KDE Frameworks Version: 5.94.0
Qt Version: 5.15.4
Kernel Version: 5.17.9-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 4 × Intel® Core™ i3-2350M CPU @ 2.30GHz
Memory: 7.7 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 3000

ADDITIONAL INFORMATION
This didn't happen in KDE Plasma 5.24, as this feature wasn't available there.