When any MTS block is placed (benches and decos), the block is always placed above the block that is looked at.

Yup, that's due to how I manually have to set the block rotation based on where the block is clicked. MC doesn't have any built-in code for rotational placement that I can use (logs have other special logic that gets wonky) so I have to make my own. Sucks, but that's MC for you. I can tweak this to pick the block better, however. I just always assumed people would click the ground to place benches and not a wall.

Fixed in V15.6.0.