Salute!
I go with Doze on this, plus last para of mm's post
As I see it, while stalled at 1g, the elevator position is a demand for a increase/decrease in G which wont be met until the AoA is such that the wing is flying again. The THS will move to supplement the SS/Elevator demand as long as this G request is not being met. Elevator at 0 equals no G demand.
Don't agree with last sentence, as a zero elevator position could result in negative or positive gee depending on airspeed and THS position, otherwise....
From what I read in the FCOM, the THS moves to reduce the requirement to hold back/forward stick. Just like non-FBW planes. So the continued back stick resulted in the THS trimming further and further. I can't find anything concerning THS movement related to measured gee, only stick position.
So I go with Doze that just letting go of the stick may have helped things at the apex of the zoom.