For unclear reasons, my default app for .djvu files was switched to "okularkirigami". 
The result was, that doubleclick in dolphin loaded an extremely limited viewer that was almost unusable, but called itself "Okular" in the title bar, in the burger-menu -> about and so on. 
Also the default application dialog showed two indistinguishable Okular applications
Only when investigating using ps x | grep okular, I found that this is a different application.

EXPECTED RESULT
These application behave are very different and should be clearly distinguishable via name in the settings, via title, via icon, and at the very least in the about menu. 

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION