Cindy
I will look to see if there is any 'code violation', I am not sure.
But in answering your question on what to do to fix it, I would at least tag the sets separately with a 'very permanent' method noting that they are fed from different buildings! Who knows what the potential difference between the 2 sets really is.
Even if this is not code, as has been mentioned many times before, code is the minimum necessary to pass an inspection.
Pierre