Strange behaviour in IndexArtwork

[Peter StreamMagic]

I know that MinimServer is very sensible for differing spelling, punctuation, and syntax. An index text has to be a 100% copy otherwise it won't be found.
Sometimes I think I am going mad in cases that I am 100% sure the index text is correct and the item doesn't show up after doing a rescan.
I then copy and paste the text and in almost all cases this does the trick.

Except in one case......?

One artist (Eerens, Ilse [Soprano]) doesn't show up in the correct way, although I copied and pasted the index text.

First the artist showed up twice:        
In MP3 Tag it showed up like this:     (what is wrong?)
I copied and pasted (accented text, other artists deleted) for all tracks:    

Result after rescan:            
For some reason the second image disappeared but the text is not correct.

IndexArtwork:     should lead to this result:         I guess.