Here is how to reproduce this bug:

1. Put a boat (any type) onto the ground.
2. Place 6 blocks on top of each other next to the boat.
3. Put another boat (any type) onto the highest block so it is above the first boat.
4. Sit into the first boat and right-click onto the top boat. The player's hand should move like entering the boat normally, but the player won't enter the boat.

A link to a detailed video explanation: https://bit.ly/2OcXQfU