I did spend some time pondering the more obvious stuff (e.g. trend towards vne) on the pitch down, but you've given me a few more things to consider. Currently I always fly trim neutral (rel to: level upright), unless climbing out, so that will have been my entry trim.
Whip stall wasn't an issue on this type - a momentary and firm nose down, but the start point was Vs obviously (55kt) and pitched up nicely at around 100kt IIRC. I felt like carrying on to prove the reducing oscillations, but we were running down on height so it felt like a good point to conclude.
Interesting to hear how things might behave. Or misbehave!
Cheers sir.