Yup, my MK 2 has that (also see my earlier post). The primary buoyancy is provided by air in the front and rear compartments and the side foam buoyancy. That’s the normal buoyancy total for the boat that keeps it afloat when hull undamaged. The side foam was put in to compensate for the half height forward compartment as compared with full height on a Mk1. The foam fore and aft is what stops it sinking if a compartment is holed. I’ve got both and I wouldn’t be without either! I think they’re built that way. Thank goodness for spellcheck or I’d never spell “bouyancy” correctly.