I've got a similar problem.
I've got 1 user who is shown online on Forumhome and his Profile page, but not on Who is online list.
The problem is that, when I was online on forum, this user showed up on who is online list for hours (even though I've closed his browser), but when I turned off my computer (without loggin out) and went to sleep, he (according to my friends) froze on who is online list. But, he was still showing online on forumhome and profil page in ten minutes' periods.
After I restarted my computer and opened my forum page, he didn't return to who is online list, but still active on these two pages.
I've no idea. Did I screw something up?