This is very true.
Quite often, you will want to slingshot papa in to the enemy lines with your DM to blow himself up and finish off what Sonnia has started, which means you want him in the box until you can move in with your Unimpeded.
After the activation flip for keeping him in the box, the only way to get him out is to target someone else with the pine box, he'll then be out regardless of the outcome as the unbury is triggered upon taking the action.
Yes, I'm guilty of running a very similar list