Hi

Weird thing happening. I have doen this on a fully charged battery and ruled out voltage failsafe (I think).
On my bench I have started up the A2 in atti mode and at first the throttle feels/sounds reponsive. Raise throttle and motors spin faster.
After about 10 to 15 minutes the throttle starts feel a little 'soft'. Raise throttle eventually the revs start to pick. Drop throttle and the motors start to spin slower but not as quickly as I am expecting.
Switch to full manual mode and throttle is reponsive again.
Am I doing something wrong?
My gains are untouched so all (basic and attitude) are set to 100. I know I need to adjust my basic gains but didn't have much time in the air to do that because after a few minutes the copter starts decending (hence why I originally thought it was the voltage failsafe and retesting using freshly charged battery).
I also tried setting throttle to mid level and left it for a few minutes, raised the throttle to full and nothing happens for about 40 or so second then it starts to pick up speed.

hexa with
2212 motors (these are about to get swapped out for either some E600's or E800's)
30A Opto's
single 6000mah 4s

Very likely this could be barometer drift.  Since it is on the bench  the altitude never changes.  In Atti mode it is trying to control the altitude.
If the pressure drifts down it will try to reduce RPM to lower altitude.  
Throttle is under your direct control in manual mode so it should always be more responsive in this mode.

Hi Joe

Thanks for the response.

What started me off to dig a bit deeper was because my copter kept dropping alititude whilst I was out in a field with it. The characteristics were very similar to what I was seeing on my bench.

I am upgrading the motors (and pretty much most of the frame) so wil take it out again next week soem time and re-test.