Created attachment 158489 [details]
a brief recording of the issue in Kate

SUMMARY

This bug is visible in multiple applications. I originally found it in the Strawberry music player (not a KDE app but does use Qt) and then later found a way to produce it with Kate. The problem is probably visible with other applications too. When you have a list of items in the GUI of a Qt application that when hovered over with the mouse result in a tooltip appearing, if you move your mouse between those items the tooltip box attempts to resize. This resize does not complete correctly though and the resulting tooltip box isn't the correct size for the text it now contains since you moved your mouse. 

I have noticed that the effect is more severe when the space between items is smaller. In the steps I provided below for reproducing the bug in Kate, the buttons are fairly large and the mouse moving a larger distance seems to make it less consistent. In the Strawberry music player though you can reproduce this issue by mousing over songs in the collection screen and the gap between them is very small, and produces even more severely buggy tooltip boxes where you can see the animation of the tooltip box resizing keep repeating in a portion of the deformed tooltip box.

There is a possibility this might be a Qt bug, but I am not sure.

Link to the Strawberry music player bug:
https://github.com/strawberrymusicplayer/strawberry/issues/1190


STEPS TO REPRODUCE

I am providing steps to reproduce this issue with Kate because it has a particular arrangement in it's GUI that makes this easy to reproduce, but it can be reproduced in other applications as well.

1. Open Kate.
2. On the sidebar on the left side of the screen, hover your mouse over one of the buttons so that a tooltip is displayed.
3. Move your mouse up or down to another button and hover your mouse over it.

OBSERVED RESULT
You should see the tooltip box attempt to resize, but it does not resize correctly. Note that if you can find another application with a list of items that when hovered over produce a tooltip with a very small distance between each item, the resize effect is even more severe.

EXPECTED RESULT
The tooltip box should resize correctly.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION