Created attachment 143126 [details]
W/ Breeze Plasma Theme, blur is not applied on the rightmost side

SUMMARY
On Wayland, whenever you move the mouse cursor from one applet to the other hovering over them, the tooltips displayed are not correctly rendered. Artifacts are in fact visible mostly on the right side of the tooltip, where translucency is applied but no blur.

This is especially visible on PlasmaThemes heavily relying on transparency and blur, such as Aritim-Light-Rounded-Blur. Nevertheless, the problem is visible, although in a less extent, also with default Breeze Plasma Theme. I'm attaching some screenshots as example.

I searched for similar issue but couldn't find anything, a part bug 422072 and clones, which I believe is deeply linked to the issue I'm reporting right now. I'm in fact experiencing that bug as well.

I'm no KDE dev but I believe the freeze on 422072 is due to this incomplete rendering, once invoked multiple times hovering over the applets many times, with a culprit on the Digital Clock (and Event Calendar).
I believe such artifacts may have been left unnoticed since on default Breeze PlasmaTheme it is quite difficult to notice them (but actually quite easy on Aritim-Light, which is a way less common Plasma Theme)

STEPS TO REPRODUCE
1. Place the cursor on Icons-Only Task Manager or System Tray applets, wait until the hovering causes tooltips to be drawn;
2. Move your cursor to hover on different task icon/applets and notice some artifacts, especially on the right side of the tooltip, indicating the tooltip is not correctly rendered;
3. Install Aritim-Light-Rounded-Blur (or any other Plasma Theme relying on transparency and blur more than Breeze) and you should notice the artifacts way better

OBSERVED RESULT
Tooltips are drawn incorrectly, presenting graphical issue on their right side. 

EXPECTED RESULT
Tooltips should be rendered correctly in their entireness.


SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20211031
KDE Plasma Version: 5.23.2
KDE Frameworks Version: 5.87.0
Qt Version: 5.15.2
Kernel Version: 5.14.14-1-default (64-bit)
Graphics Platform: Wayland
Processors: 4 × Intel® Core™ i5-5200U CPU @ 2.20GHz
Memory: 7,7 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 5500

ADDITIONAL INFORMATION
This bug may be related, with way more drastical consequences, to bug 422072. It also may give devs further information and help them finding the cause, which may rely on the (bugged) rendering flow applied to tootltips