Holding scaffolding in the off-hand will change the hitbox from a normal block to scaffolding's model

1. Put scaffolding into your inventory
2. Place a block at eye level
3. Transfer your scaffolding to the off-hand.
4. Place another block looking at the side of the block, aimed in the centre.
5. Block will not stack on top, but placed behind instead.

This might be intended but I can't see any utility for it.