Created attachment 156370 [details]
Bar across entire top of panel

SUMMARY

This is new with 5.27. Tiling a window (or maximising it) results in a bar across the bottom of the window (see screenshot). It's not always flickering, but the flickering seems to correlate with mouse movement. Note that there is a bar across the entire top of the panel, that's definitely new - I looked at a screenshot from a few days ago to confirm.

STEPS TO REPRODUCE
1. Put a panel on the bottom of the screen
2. Tile any application (I used Firefox - native Wayland or xwayland doesn't seem to make a difference)
3. Observe flickering bar at bottom of window.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Linux 6.1.12-arch1-1
KDE Plasma Version: 5.27.0
KDE Frameworks Version: 5.103.0
Qt Version: 5.15.8

ADDITIONAL INFORMATION
I'm using the open-source AMD driver and Wayland. I also have multiple monitors, and the problem appears on both. I am not using the new custom tiling functionality.