Thank you Lespaul for working on this - apparently - special Problem...
"Keith Jarrett\\Charlie Haden" is NOT a Folder structure, it means, that I have two artists in the meta-data of each track in this folder.
To explain the behavior in detail, I have three Folders:
e:\Musik\Keith Jarrett\1975 - The Köln Concert [24-96] [+0,5 dB]\
e:\Musik\Keith Jarrett & Charlie Haden\2010 - Jasmine [24-44]\
e:\Musik\Keith Jarrett & Charlie Haden\2014 - Last Dance [24-96]\
If I choose the "Köln Concert", I get only the associated "Booklet.pdf"
If I chosse "Jasmine" or "Last Dance" I get all the three booklet.pdf from the three Folders shown above
I hope, this gives you additional information to fix the Problem...