Why would the treadmill tell me this?

Question

I was running a cross country program this morning on a treadmill at the gym. I ran for 32 minutes averaging 6.2 miles an hour which works out to 3.31 miles. After the 32 minutes I did a 5 minute cool down walk around 3.5 miles an hour. I am a college graduate so know the total miles ran is around 3.75 miles.

The workout summary said the total distance was 7.49 miles. I don't understand this and the only reason I can think of was that the elevation kept changing as I ran.

Does anyone know why the treadmill would do this? If so, is there a formula used to establish the "percieved" distance?

Thanks!