That's because it has been answered many times already. Just read the Yellow test thread's main post. If you read all the pages you'll see it has been answered at least 3 times.
Yes, some refurbs do infact have the said issue at least it's the case for the first batch of 21.5" iMacs. It probably means that this isn't on Apple's QA yet. Or they simply haven't figured out what was wrong with them.
Now I am curious about the more recent batches — whether or not they still have the said problems.