Created attachment 170665 [details]
Screenshot showing the incorrect background near the floating panel, toward the center

SUMMARY

If a floating panel is repeatedly moved between screen edges (in particular from bottom to the sides), the background colors are not correctly set. Usually the first move seems to work, but repeating the same move seems to reliably trigger the issue. 

This is replicable on a completely fresh user account on current Neon.

STEPS TO REPRODUCE
1. Start with the default bottom floating panel
2. Right click the panel, "Show Panel Configuration", click Position, click the arrow pointing left, click Done
3. Repeat 2, this time clicking the arrow to the bottom.
4. Repeat 2.

OBSERVED RESULT

The area next to the floating side panel (toward the center) does not match the desktop background at that point. (See attached image).

EXPECTED RESULT

The area around the panel matches the desktop background, as it does after the first move.

SOFTWARE/OS VERSIONS

Current Neon

KDE Plasma Version: 6.1.80
KDE Frameworks Version: 6.4.0
Qt Version: 6.7.0