Wrong tags in twonky

I use twonky 7.2.8 as media server on a qnap nas.
I have some flac files which tags are not correctly displayed. I suppose this is because some fields contained special characters.
For instance I ripped the cd of robin mckelle, heart of Memphis.

The default tags were:
Artist: robin mckelle & flytone
Album: heart of Memphis
Style: jazz

Using mp3tag software or dbpoweramp, I changed theim into:
Artist: robin mckelle
Album: heart of Memphis
Style: vocal jazz
But in twonky always display the old tags after data rebuild?

I also tryed to remove all the tags including cover art and re-fill all the fields but old tags are still displayed in twonky.

I also tryed to convert my flac into wav in order to loose the tags and reconvert theim in flac, but old tags are still displayed in twonky.

Finaly, I opened flac files with an editor software and I saw that there are several other artist, album, style... fields contained in the begining of the files. I tryed to change the wrong tags and saved the files, but the files are not playable anymore.

Any suggestions to remove these tags?