Registering a player to an island does not update the old owner's file

[BlackBeltPanda]

Please paste the output from /usb version below

Name: uSkyBlock
Version: 2.7.3-alpha13
Description: Ultimate SkyBlock v2.7.3-alpha13-f55f3d-448
Language: en (en)
State: d=500, r=152, i=1,546, p=12,576, n=false, awe=true
Server: Paper git-Paper-916.2 (MC: 1.10.2)
State: online=true, bungee=true
------------------------------
Vault 1.5.6-b49 (ENABLED)
WorldEdit 6.1.3;7a097ca (ENABLED)
WorldGuard 6.1.2;e38d98d (ENABLED)
FastAsyncWorldEdit 16.11.17-e16bcae-372-9.11.4 (ENABLED)
Multiverse-Core 2.5-b719 (ENABLED)
Multiverse-NetherPortals 2.5-b710 (ENABLED)
------------------------------

What steps will reproduce the problem?

1. Register a player to another player's island with "/usb island register "
2. Island updates with new owner and member list is cleared
3. Previous island owner's/members' files are not updated so they still have access to "/is" menu on the island but cannot leave it to join a new one.

[Muspah]

There's more related to this issue, I've seen problems a few months ago with multiple island files in storage for the same island where things like trustees from the old island storage file got trusted on the new island.

But that's just a note for future reference if we can reproduce it.