SUMMARY
I've set the panel containing the taskbar to "auto hide".
I've disabled in _all_ notifications/event sources "Mark taskbar entry".
After "Minimize Windows" and show again, taskbar entries _are_ marked and thus the panel is un-hidden until I manually select each taskbar entry.

Thus the whole purpose of both deselecting "Mark Taskbar Entry" and "Auto-hide Panel" is defeated.

It's not true for all applications, though, but usually Firefox and Eclipse.

STEPS TO REPRODUCE
1. make sure in Notifications setting to disable "Mark taskbar entry" for all and sundry
2. set panel with taskbar to "auto hide"
3. add "Minimize Windows" applet to panel
4. click "Minimize Windows" - all windows disappear
5. click "Minimize Windows" again, windows reappear - taskbar entries for some applications (Firefox and Eclipse in my case) are marked
6. panel does not auto-hide until I did click all marked taskbar entries

OBSERVED RESULT
taskbar entries are marked, panel does not auto-hide

EXPECTED RESULT
no taskbar entries are marked, panel does auto-hide

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

ADDITIONAL INFORMATION