Every spitfire has this habit, except the 16 with its shortened wings. At least after the 109/190, i felt something simmilar to the 152's stall.
This flat stall might be especially tipical for the Spit I because its relatively weaker engine combined with the faulthy carburator design, once you get into this situation, there is no engine power to "pull the plane forward" from the stall. Also, as you have mentioned, the CoG might be further back then no the other Spitfires.