What I expected:
I edited the sounds.json file to include multiple entries for title music tracks. I expected that it would pick a random track and when finished it would pick another random track.

What actually happened:
What actually happens is that one track starts playing and then another track starts playing shortly after on top of the first track so that they're both playing simultaneously. It seems to be limited to only two tracks at a time, though.

Steps to reproduce:
I made a resource pack with a custom SOUNDS.JSON file which included about 7 entries in the title music category. They are correctly defined and Minecraft recognizes them (obviously as they play fine, just on top of each other). I then started up the game and waited for the first track to start. It does (it also seems to be the same track every time, instead of being randomly selected as I had hoped). It then plays the second track on the list a few seconds later

Attached is my sounds.json file.