Found a few bugs last night, Attack of the B-Team modpack. Sync version 2.1.0

1. Leave a shell in the Nether, log out, log back in, shell is gone, overworld shell is still there, as well as the original. -Repeatable
2. Don't know if its a bug but ender chest (Vanilla) inventories are not accessible by shells and they all seem to have separate ender inventories. But the tinkers construct knapsack and heart canisters transfer over between the shells without me transferring the actual items.
3. Experience levels were copied over, each shell is receiving 47 levels, which is what the original had at the time of copying the first, but not the second shell.

For the second one, the ender chest thing is not a bug. Ender Chest inventories are stored in the player's NBT data, as opposed to the chest's. Since each shell has their own separate NBT data, of course they would have separate inventories. Not sure about the knapsack though.

Point 2 and 3 have been fixed. Point 1 is being harder to track down, can't replicate it properly. Seems to be random and currently investigating

Cannot replicate it in 2.2.0/2.2.1 any more, seems to have been fixed.