worlds with singleplayer_uuid different than the user's fail to save

Worlds with the singleplayer_uuid field set use that uuid rather than the current instance's player's uuid to load the playerdata. However when the player then saves and quits, it doesnt save their data back to singleplayer_uuid.dat, nor does it update singleplayer_uuid field to match the new players. So the next time the world is loaded it ignores the players uuid.dat save and pulls up the same data as the first time it was used

Steps to reproduce.
Create world on user1
Send world to user2 (or edit uuid of playerdata and singleplayer_uuid)
Open world with user2, change something, save and quit
reopen world