I have many bugs to do with boats. I found these while trying to make a mario kart style game with boats. In this, I wanted to be able to teleport boats with players in them. This turned out to not work at all. This was in 1.11.2 and continues to fail in 1.12.

Using /tp @e[type=Boat,r=3] ~ ~20 ~ while in a boat did not change its position, nor if u change any of the x y z values.

To replicate this first bug, do the following.

1. Spawn a boat (on land or water)
2. Get in the boat
3. Run this command: /tp @e[type=Boat,r=3] ~ ~20 ~

But this is only half the problem. Trying to add Motion to the boat also fails. I wanted to use this as a Boost Power-up in my game, but changing the Motion tag only worked with no Player within the boat.

To replicate, do the following:

1. Spawn a Boat
2. Get in the Boat
3. Run this command: /entitydata @e[r=3]

When out of the boat, it flies away with high velocity. When in the boat however, nothing appears to happen. To continue some testing on the boat, I also tried to apply an effect on the boat, to which it said it could not find the boat. To replicate:

1. Spawn a Boat
2. Run: /effect @e[type=Boat] speed 10 1 true

After these 3 Bugs, I found it necessary to report them as this was once possible (apparently) before 1.9, which it now doesn't work. I have looked at other Issues on this site, but they seem to be falsely resolved. I therefore hope it is resolved and fixed soon so I can use these within my commands.