Attempting to place scaffolding on a structure block (while sneaking) will not place the scaffolding. The scaffolding also turns into its suspended model when attached to other scaffolding, while on top of a structure block.

To reproduce, simply try to place scaffolding on top of a structure block while sneaking.

Expected Results:
The scaffolding is successfully placed on the structure block.

Observed Results:
The scaffolding cannot be placed on the structure block.