shulkers in boats turn black they are still alive etc but they appear black. they can also glitch into the block under the boat when the boat is broken.
other mobs in boats are also kinda broken.
endermen, zombies, skeletons (things with legs basically) stand up in boats after being in the boat for a while(or being unloaded) they are still in the boat just standing up.
spiders will not get into boats. they instead break the boat. or put it back into your hotbar.
more boat problems!
when placing a boat under water it sinks to the bottom of the water instead of floating to the top like before. idk if this is a bug or intended.