At this moment there’s a problem with “Who’s online”
The names of the members being online isn't always accurate. We have contacted support at UBB threads. Keep you posted.
The one that shows on the main forum is cached; as in it won't always update on every reload. The other (full page) is not cached, and will always display things "live". That's the info I have received from support.
If you click "details" at the bottom of the page (in the section who's online) then you'll get an accurate view on who is online at that moment.