During a recent remodeling of my bathroom, I discovered a HVAC plenum box underneath my subfloor (second floor). I noticed that the supply plenum box does not have an exit flexible duct. It’s connected to the floor joist facing down into the kitchen ceiling. It appears the contractors covered up the box with the ceiling Sheetrock. I also notice the cold air coming out from the base, not a good seal with the Sheetrock. My question is, should this be like this or should the box have been removed and the flexible duct sealed? Would their be reason, other than being lazy, why the contractor left the box like this? The box is 12 inches squared. Thanks