Is that a GT hull?
It is the same bottom as mine, and they do really weird shit on a hard shutdown, submarining is not one of them. Look for a squishy area in the bottom of the hull just in front of the engine, you may need to stiffen things up a bit.
When I shut mine down hard for the first time from about 80mph, it pulled really hard to the left and took a little water over the right rear, but the bow never got wet. My shorts however were a little on the moist side... A drip or two of pee did escape...

GT