When I was testing my newly acquired IC-765 last Christmas, I had some troubles with the built-in antenna tuner. From time to time, it would start re-tuning the antenna in the beginnig or even the middle of my transmissions.
In the VE7HUR notes on the IC-765, there is a problem described concerning the SWR sensor circuit becoming too sensitive after some time and I truly believed that this was indeed the problem with tuner. This time, however, I did not have a single automatic re-tune, so now I believe that the tuner is all right and it must have been the antenna, which was changing all the time. It wouldn’t be too surprising with such an old antenna. I will investigate it further when the winther snow has melted.