If you're wondering what the deal is and whether or not we're aware:

We are.

There are several topics in Site Feedback where you can voice your experience or read up on why it happens. Essentially it's caused by minor corruption in the forum database but ramirez has made a few tweaks and may have solved the problem. Time will tell but someone suggested posting this which isn't a bad idea.

To quote the great "Blizzard Entertainment":

"We are aware of this issue and are currently working on a fix. Unfortunately, we do not have an ETA regarding this matter. We are sorry for any inconvenience this may cause and hope to see you soon in the World of [Gaming]."