I would recommend testing with another PSU first, just to be sure, but yes, it does sound like you have a bad motherboard to me.
You could probably ignore it if you wanted, this sounds like a very simple short, and is unlikely to cause any significant problems aside from being annoying. Up to you on that point, but it should be a valid RMA issue.
Feel free to contact me at the email in my signature if you have any issues with the RMA process. I'll see what I can do to smooth things out.