Thanks for your suggestion, ColeenD3. I did double check on the forms that were listed in my question. The W-2G and K-1 forms do not exist in my return (I created then deleted the forms just to make sure). I have no W-2 income, so the excess Medicare withholding likewise does not exist. As far as I can tell, there is no entry on my part that corresponds to the value in the printed 1040.
