you probably set your username to be hidden from your profile, make sure it's unsetted that option

if it's not that the problem, then i have no clue, perhaps a moderator/forum adminstrator will answer you, but i truly doubt it's a bug as it works for me pretty well, i can see whether or not i am online and logged in on the forums if im not an hidden username, but currently im an hidden user as i setted on my profile to be like that

but then again, make sure your username is not setted as hidden.
