After another weekend away and a couple more TA interruptions, it seems that traffic announcements work correctly in Tuner mode (including returning to the original programme at the end), but I've had no success in Player mode. It seems to give a burst of the traffic station, then switch back to the usual radio station immediately.

The performance of AF following whilst in Player mode seems a little flakey; I don't know if this is related to the problems with presets?