I think I've finally figured out why this is occurring.

I'm using the following URL to get to FlyerTalk:
http://www.flyertalk.com/forumcgi/Ultimate.cgi

If I use the "back" button on my browser to get the the FlyerTalk home page, I'll sporadically have the problems with lightbulbs I described above.

If, on the other hand, after the first time I go to a forum, if I navigate to the FT home page by clicking on the FlyerTalk 6.0 link at the upper right hand side of the browser window (the one with a picture of a yellow folder next to it) instead of using the browser's back button, I don't have the problem, even if I use the browser's back button at any point after that to navigate to the FT home page.

Note that when I navigate to the home page the way I have described, the URL in the address are of my browser window reads:
http://www.flyertalk.com/forumcgi/Ul...assCookie=true

whereas if I only ever navigate with the back button, it shows as:
http://www.flyertalk.com/forumcgi/Ultimate.cgi

I don't know if there's any way you can fix this with a UBB setting, but I'm at least glad I found a workaround. This thing's been driving me nuts for months. (OK, I'm easily driven to distraction!)

Hope this helps.