Ian,
I should have recognized the symptoms. Some years ago I had a couple of customers in New Zealand and I had to keep in mind the time difference of 3, 4, or 5 hours (plus 1 day) depending on the time of year before calling them.
So if I want to keep the reported time in sync with my local time, I need to adjust it every time either country switches between standard and daylight time. Or switch the forum to UTC as you suggest.