SUMMARY
If hovering over an html file, there will be a not contained popup with the preview shown, which is supposed to be shown in the side panel.

Meanwhile the following error will be logged on the console:

```
qt.qpa.wayland: Creating a popup with a parent, QWidgetWindow(0x5....0, name="Dolphin#1Window") which does not match the current topmost grabbing popup, QWidgetWindow(0x5...0, name="QMenuClassWindow") With some shell surface protocols, this is not allowed. The wayland QPA plugin is currently handling it by setting the parent to the topmost grabbing popup. Note, however, that this may cause positioning errors and popups closing unxpectedly. Please fix the transient parent of the popup.
``` 

Sometimes the popup will show up multiple times, which makes me believe there's another bug that the preview will be actually created multiple times instead of just once. In addition the preview doesn't seem to be stored at all, and instead be recreated on each hover - which is quite a performance concern.

Apart from this these popups sometimes also happen if Dolphin is in the background and other windows cover it. Leading me to believe that Dolphin under Wayland currently does not recognize that it's moved in the background and will render popups regardless, just because the cursor is hovering over files (while another window is covering it) - which is another performance concern.

These popups can completely be avoided by turning off html file previews in the Dolphin settings.


STEPS TO REPRODUCE
1.  Save a website in a folder
2.  Run KDE under Wayland
3.  Open Dolphin
4. Hover the html file


OBSERVED RESULT
See uncontained popup

EXPECTED RESULT
No uncontained popup

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
KDE Plasma Version: 6.3.3
KDE Frameworks Version: 6.12.0
Qt Version: 6.8.3

ADDITIONAL INFORMATION
Have been reported by u/ReadingThin3038 and u/Attacktive on Reddit as well:

https://www.reddit.com/r/kde/comments/1jcgbt2/dolphin_shows_popup_preview_windows/

SCREENSHOT

See redit post