There were articles in the major newspapers about this. It was on Bloomberg.
Cheaper Mortgages Spark Lower FICO Scores for Payers (Update1) - Bloomberg.com
The details from the story are pretty clear:
“We view an account that has been settled or renegotiated for less than the full amount as a negative because historically consumers on reduced payment plans represent a greater risk,” said Ethan Dornhelm, a principal scientist at FICO’s San Rafael, California, office.
Personally, while I can understand that a borrower might be a more than a little upset at such a result, as it could cascade into reducing credit limits and/or increased rates on variable consumer borrowing, the fact is FICO exists to help LENDERS make decisions about managing risk. By readjusting amount to lend / rate to charge these changes tend to make things safer and keep credit working.