Here's a thought that occurs to me. If you have the weight of the flooded bow section cantilevering the stern upwards, when the keel fails and lets go, is it possible that the change in the Center of Gravity could cause a sudden forward rotation of the bow section?
In other words, keel section fails amidships, bow and stern are now functioning as two separate boats precipitously connected by shell plating around C-B deck level (if the Mengot "Hinge" theory is right) and the forces of gravity acting on the bow section shift dramatically. Suddenly the weight of the stern section is off its back and the CoG shifts forward in the bow section, causing a rotation where the flooded nose plunges and the semi-dry midships section snaps upwards, giving the illusion of the bow section rising as a whole.
That is plausible to a small but possibly perceptible extent on the deck. The stern of the bow, in short, rose, which was part of the bow section; I often think that the small number of people who said the ship broke in two and the bow rose aren't taking about a V-break but rather what you describe (which is literally the bow section rising, most of the quotes meet that definition), I've never looked hard at it to rule it out or not, though.