SUMMARY
KDE 5.18.2 from kubuntu-ppa:

When selecting a menu item the wrong menu sub menu item often is marked as active.

STEPS TO REPRODUCE
1. e.g. choose "Workspace Behavior"
2. In the sub menu select another item than the first one. e.g. "Screen Edges" (this is the third item)
3. Choose another main menu item, e.g. "Window Management".

OBSERVED RESULT
Two sub menu items are marked with a blue back ground. The first item (which is correct as this is the active one). And the third menu item, because I had selected the third menu item in the other main menu before. If you had selected the 4th sub menu item before, the 4th menu item would be selected now. (and so on with the n-th item.)


EXPECTED RESULT
Only the first sub menu item should be marked as active.

SOFTWARE/OS VERSIONS
Operating System: Kubuntu 19.10
KDE Plasma Version: 5.18.2
KDE Frameworks Version: 5.67.0
Qt Version: 5.12.4
Kernel Version: 5.3.0-40-generic
OS Type: 64-bit
Processors: 8 × Intel® Core™ i7-2600K CPU @ 3.40GHz
Memory: 7,7 GiB of RAM

ADDITIONAL INFORMATION
Used Global Theme, Plasma Style, Applicaton Style and Window Decorations: Breeze.