No Autotrim At Stable Speed ? / Nullzone Issue ?

Hi

I think the trim reference speed work as it should, but i'm having an issue with the autotrim though.

yesterday i was performing a standard ILSZ APP at FMEE after caturing the GS and stabilise at the VREF 20 speed ( approx 160 kts) I disengage the AP.

I then select Vapp= 148 on the MCP and select flaps 30, I use the trim, when i was close to Vapp I double clicked on the trim so that the blip trim goes into action, so the trim reference speed was at Vapp. 

I then pitch up to maintain the flight path, the AT increase the engine N1 to maintain the speed but when I released the yoke the flight path wasn't maintained, the ptich was slightly dropping. I often double clicked on trim to make sure that the trim reference speed was at the current Airspeed of the A/C.

But if I rememer well the FCOM

when the yoke is released :

the flight path is maintained provided the speed hasn't changed.

autotrim also when config change, gear up/down and thrust change.

Alsoi notice that in bank, the flight path is only maintained if the Bank angle is between +- 15°, when I go up to 30° the vertical speed drops to -800 ft/min assuming fying level prior to the bank. I haven't test for the config changes.

I'm using Thrustmaster Tflight hotas X, default nullzone setting in the CDU, minimum sensitivity and nullzone in FSX controller setting.

This evening will set the axis on FSUIPC instead of FSX, will see if it makes a difference.

Will also provide a video.

Any ideas

Thanks

CMB