Awesome engine!
It looks that it's really well written.
I can imagine how hard would it be combining all these things you have said (sloping system, knockbacks, etc) fully compatible with each other.
As far as I know and seen, when dragging dynamic object in HPL and HPL2 the anchor point isn't attached to the position you have clicked.
In case of dragging it is but not when you walk while holding an item.
Example:
It's not that important but it gets difficult when pushing heavy objects. You basically can't rotate them.
Tell me if you get my point.