Just had a thought.
Grappling a ghost. Could they pass through the person attempting to do so with insubstantial instead of attempting to break free? Or would it work like melee attacks? Able to do so due to being a living person with chi flowing through them.
Also, hitting a ghost with iceblast or anything that requires a strength check to break free from. They could essentially pass through those things too.
I mean, being able to pass through walls and rocks, but not a encasing of ice (when ice isn't on you "do not pass" list) seems pretty groan-worthy to me.