I started checking their control inputs during the control checks on the ground and every time their roll inputs also induced pitch inputs ie ailerons full left and there would be some up elevator, ailerons full right and there would be some down elevator. Once I brought it to their attention and they adjusted their hand wrist positions and tried again (calibrated their senses) so that they could make "pure pitch" and "pure roll" inputs things went a lot better during manual flight.
I'm not a pilot and this could be a load of rubbish, but perhaps the control laws play a part as well. You're taught on 'traditional' aircraft which require back-presure (pitch) to maintain altitude when rolling. Maybe this sub-conciously transfers over to the Airbus?