Motor problems - help and advice requested.

[Area21]

I have been operating a Sky Jib X4 Ti QR very successfully for quite a few years now with no major problems until yesterday whilst undertaking some pre- flight tests before the next filming job !  Fitted with the DJI A2 system, Futaba 14sg transmitters.
First thing to notice was on start up only 4 of the motors started (2 counter rotating pairs).  This has always been all 8 start together.
Increasing the throttle started one more pair and by increasing the throttle to almost take off stick position the last pair of motors started.
Being not happy I shut the motors down.
Disconnected batteries. 
Tried again and only 4 of the motors started with the other 4 motors starting immediately as I increased the throttle.
All motors running and up to take off speed I lifted off in to a hover.
Everything looked and felt fine. Continued to hover for 5 mins and then flew around cautiously for another 5 mins and landed.
Turned everything off / disconnected both batteries. Had a coffee + +
Reconnected both batteries and prepared to take off.
Again only 4 of the motors started, then another pair started and then the last pair.
Just as i was getting up to take off speed, one pair of motors stopped and I was quick enough to shut the motors down to prevent it toppling over.
I flew this externally successfully recently and the UAV has not been folded up, packed away and is just as it was.
Any ideas would be really welcome?
Adrian.  http://www.skycaptain.co.uk/

[Cheredanine]

Recalibratenescs?

[hoverfly]

My thought as well.

[Area21]

Recalibratenescs?

Many thanks - will do this at the weekend and re-test.