Thanks for bringing that to my attention, Thump. I was beginning to think you were hallucinating until it finally happened to me. I found a tag in the header section for the forum portion of the site that was causing the page to refresh after 5 minutes. I have no idea what it was doing there - I must have been experimenting with something last year - and there was no need for it, so I've deleted the line and that problem should be gone now.
Interestingly, that refresh tag apparently only worked in Firefox. Chrome and IE both ignored it.
One bug down, but still more to track down and fix - there's no rest for the wicked.