Riding an entity (boats, pigs etc) through an end portal will cause weird and slightly inconsistant behaviour if the exit point is in an unloaded chunk. 

Note: a player on foot can traverse the End gateway regardless of distance to exit.

Repro steps

1. Load a superflat world in creative mode.
2. Lower Render distance a bit, so that far away chunks are unloaded. 
3. Use the following command:* /setblock 110 4 -90 minecraft:end_gateway{ExactTeleport:1b, ExitPortal:{X:1450, Y:5, Z:1770}} destroy  *(Note the coordinates may change for you, but the important part is: Portal close to you, exit far away from you).
4. Go through the teleport on foot to verify that it works and teleport back if it does. 
5. Spawn a boat, enter it and try to row through the portal. 
6. Notice that the boat will either row right trough the portal block without being teleported or that it will get stuck in the cube, with the camera spinning uncontrollably and the player being unable to exit the boat.

Expected behaviour

The player should be able to use the End portal even when travelling/riding another entity. 

Additional information

• If the player saves and exits the game while spinning in the End portal cube, and then enters the game again, the boat will now have gone through the End portal and can be found at its exit destination. 
• Boa

• If the ridden entity is carrying cargo (shulkers or pigs), the boat will teleport out of the "spin" upon exiting and re-entering the world, but the cargo will disappear.