From the GM/Moderator that replied to your thread:

Hey there LittleArrow!

Sorry to hear you've been having that problem since Beta. We appreciate you contacting us back so quickly with a response. Since you've taken several steps to ensure it's not the graphic card, we'll gladly forward the concern to be looked into. If there are any updates on the matter, it will be posted within the forum. Thanks for posting!
They closed it because it was brought to their attention, they've acknowledged it, and are forwarding the problem on to whoever in SE might deal with that.

As they said, if/when there's a solution, they'll post about it. Those forums aren't meant for discussion really, so they need to keep threads locked once acknowledged so that new threads coming in don't get overlapped by old & already acknowledged threads bumping up due to discussion.