OK then
I found out now

problems with refreshing after deleting/adding of mediafiles
-"tracker-processes -r" is enough to refresh to the exact number or the names of files.

problems with bugging albumart pics
-1- in the music dirs: delete/move away the pics you don't want to be associated with the music files in the same dir
-2- in home/user/.cache/media-art/: delete (specific) pics, this to clean more thorough, because tracker will have left copies there too.
-3- under home/user/.thumbnails/: delete (specific) pics, this to clean more thorough, because tracker will have left copies there too.


Do the above at your own risk (I would reckon some non-graphic .cache-files are to be left untouched and I do not know everything of it).

The more you delete the more tracker has to extract afterwards. I deleted them all in a rage, and I see now that the thumbs are restored in Mediaplayer s l o w l y and with considerable CPU-power being consumed.