You can stack up to 2-3 Shulkers in a Shulker now so that's worse.
Although if you have 2 side by side broken shulkers and you add another into another one it will cancel out the other shulker and revert it back to a normal shulker.
Yes the problem still persists on 1.11.1
I assume the shulker decides to place itself to whatever pos the boat is in, but it places it a bit to low. Maybe have a function check if it is a shulker in a boat and if so place it higher?
Anthony Wu this bug is also in 1.11 and 1.10 this bug has been known for a while.
Also capes are given to those who Mojang believes deserve a cape.
Cheers -Raf
More Updates on Issue
These 2 demonstrate a regular spawned shulker that teleports when you push a piston into it.
Minor Update:
Sometimes the shulker box replaces the block it goes into and that block is gone forever.