I've had this issue for quite a while now. I minimised all the forums on the main page and closed the browser, now I don't see any image to click to make 2 particular forum groups reappear any more, namely:
The Marketplace
Web Site Development
All the rest appeared back as normal once I clicked the small button in the top right again. Anyone have any idea? I've not looked into it, and as previously stated, it's been like that for over a month now. I'm not overly concerned, but it is a bug which I'm sure could happen to anyone.
Anyone relevant input would be more than appreciated.