Report in UK GASIL 04/2003.
A 'recently manufactured' aircraft fitted with a KAP 140 autopilot was collected from maintenance, and when the pilot dialled in a left turn, he found the bank angle and rate of turn were much less than expected; he then tried a right turn, and found the aircraft rolled rapidly to the right, well past the usual angle of bank.
A mobile phone in the baggage hold was found to be switched on, and when it was switched off, the A/P response became normal.
Not conclusive, but it's not the sort of thing you want to discover if departing in IMC and engaging A/P soon after takeoff.