The code M for the offset distribution simply extends the rollover deadline from the normal 60 days to the due date of your tax return, including extensions. The sum of these two Forms 1099-R represents the total amount distributed from your 401(k). Both Forms 1099-R must be reported since both represent money distributed from your 401(k). The amount that was reported on the code M1 Form 1099-R was turned around to pay off the loan.
