I think this may already have been reported a while back, but just in case it hasn't, there seems to be an issue with 'Helpful' going missing .
Basically, sometimes when in the Activity view, if I click on 'Yes' for Helpful, it doesn't turn green. My workaround was to click on the discussion or blog post (so that I was no longer in the Activity view), and then scroll down to the comments and reattempt. However, this doesn't seem to be working when I tried it at this page:
When I clicked on it, it turned green, as shown here:
However when I refresh the page, the Helpful is gone : (
It's a minor issue of course, but just wanted to report it in case it hasn't been so far.