The bug

If you just right click on a structure block while holding it it will place another one next to the block and also open the interface.

How to reproduce

1. Restart the game
2. Create a new world
3. Create a nether portal
4. Go through the nether portal
5. Go back through the nether-side nether portal
6. Give yourself a structure block
7. Place the structure block
8. Holding a placable block, right-click the structure block