Credit for finding this bug goes to Emanuel Armasoiu (testing on Samsung Galaxy Mini 2 Android 2.3.6)

I confirmed on Samsung Galaxy S4 Android 5.0.1 MCPE 0.12.3 single player. All methods below work in survival and creative.

what happened:

First method

1. place a boat near to the wall that you want to walk through so that the boat is partially in the wall (see the image original find.png)
2. Board the boat
3. Leave the boat (or you can destroy it)
4. Walk directly into and through the wall
   If you walk through quickly, you take little or no damage in survival.

Second Method (images 1-5 creative, 6 in survival)

1. place a boat so that part of it is inside the wall
2. Board the boat and press both arrows at the same time until you "paddle" through the wall
3. Leave the boat (or you can destroy it)

I expected boarding a boat that is partially through the wall would not let you pass through the wall. Alternatively, I expected that placing a boat partially in a wall would "bounce" the boat out of the wall or would not let you board the boat.