I believe this was an oversight when first introducing the new Update Aquatic music into the game. The way music is supposed to work in the game is to first play music to the player, wait until the music ends and then play another after a brief period. However, the music for update aquatic is supposed to be biome dependent (it should only play if the player is in any river or ocean biomes) like the nether update music, not dependent on what block the player is in. The easiest way to reproduce this bug is to be in Creative mode and wait until music starts playing in the background. 

Steps to Reproduce:

1. Create a world in Creative mode. Immediately music should begin to transition from the Main Menu music to one of the music tracks for when the player is in Creative mode. (Make sure the volume slider for music is turned all the way up to be able to tell)
2. After you can hear the background music playing, find some water that was naturally generated IN A OCEAN BIOME.
3. Submerge your player into the water.

Observed Results:
Any background music gets immediately interrupted and one of the three tracks of Update Aquatic start playing.

Expected Results:
Any background music would continue playing. And once it ends, one of the three Update Aquatic tracks should begin playing after a short period.

Screenshots/Videos attached: Music test.mp4

Notes: It is critical to know that you will not be able to reproduce this bug just by finding water in a random pond or by using a water bucket.