Hi MASH up to y2000 I was ione of a handfull of Avionics specialists with Civil Aviation Safety Authority (Australian equivalent of CAA or FAA) and was aware of the reports from other authorities. My ongoing belief was that it was all a beat up though I would never buck the party line of conservatism. There were not the same restrictions on electronics in small aircraft primarily because the pilot was aware of the activities of each passenger but again no reports of interference in this area. Perhaps in this case they didn't bother to report just tell the passenger to turn it off.
To add to others comments. Of course low level flight is far more critical. Especially if you consider that instrument landing systems are connected directly to the autopilot in cat 3 case to take the aircraft to ground level. That is certainly no time for a glich. olewill