While attempting to go through the end portal using a piston and a wall, I found myself teleported to my overworld coordinates – but in the end dimension. 

Steps to reproduce

1. Clear the lava pool under the end portal (if attempting it in a stronghold).
2. Place a wall 3 blocks below the end portal, so that you can stand on it without being teleported.
3. Place a piston 1 block above the wall and 2 blocks away in any direction, piston must be facing the wall so that you can stand in the middle while being two blocks below an end portal. (Do this so that the piston will push your lower body towards the wall)
4. Stand close to the piston, on the empty space between the piston and the wall.
5. Power the piston.

Observed behaviour

Player gets teleported to it's overworld coordinates in the end dimension

Expected Behaviour

Player gets teleported to the obsidian platform in the end