I have submitted this in a bug report, but I wanted to post it so other people would know to avoid it. I didn’t lose my streak, but who knows, maybe I just got lucky. A person could also easily get confused, hit refresh, and try to start pwning threads again which would ruin their streak.Basically, don’t check the almanac after you have pwned the last thread just before leaving the forum. If you do, and you get the error message saying you left the forum, just leave.

I found out if you try to check your almanac after you pwn the last thread, but before you click the link to exit the forum, the almanac will not pop up. It will tell you you have the left the battle without completing the forum.

I was scared at first that I had lost my streak, but it turns out I did not. So apparently this bug is just a minor visual error and does not affect the actual gameplay.