[sciurius]

A couple of test runs.

Server is Samsung GT-N8010, LineageOS 14.1 (Android 7.0). MSPro does not manage song files. Config is to update client only.
Client is Asus Zenpad Z300M, Android 7.1. MSPro manages song files.

First run: The status of the client is arbitrary, so many files are updated from server to client.
Second run, immedeately after first: A number of files are, again, updated.
Third run, immedeately after second: A number of files are, again, updated.

For example, take a look at "----- Set 1 -----.pdf", a file that definitely didn't change since its creation.

Also, watch "The_Parting_Glass.cho". There are 4 (different!) files on the server:

-rwxrwx--x 1 root sdcard_rw 991 2018-05-23 19:35 Folkmuziekgroep_Drenthe/The_Parting_Glass.cho
-rwxrwx--x 1 root sdcard_rw 908 2017-07-28 21:07 September/The_Parting_Glass.cho
-rwxrwx--x 1 root sdcard_rw 897 2017-06-16 15:59 SingAlong/The_Parting_Glass.cho
-rwxrwx--x 1 root sdcard_rw 941 2018-05-01 12:10 Songs/The_Parting_Glass.cho

However, they all end up in a single file on the client:

-rw-rw---- 1 u0_a132 sdcard_rw 991 2018-06-25 13:21 The Parting Glass/The_Parting_Glass.cho

Log files (each file includes all 3 runs) attached.

EDIT: Much to my surprise (and astonishment) I found out that when restoring a full backup, the collapsing of songs with identical names into a single song file also happens.