How can average speed be greater than max speed?

I had a bunch of students race with my Garmin Forerunner 910XT today, and the results for very strange. For literally each one of 15 iterations, their Average Speed was listed as HIGHER than their Max Speed - by considerable amounts. And of course, it's impossible.

AvgSpeed MaxSpeed
16.2 6.6
17.4 6.4
23.1 9.6
22.9 6.6
23.6 7.7
25.2 7.4
25.0 7.5
16.2 5.9
23.1 8.2
28.1 7.6
22.6 8.5
19.4 6.8
18.0 6.6

Might anyone know why? I thought it might be a difference in units, but this discrepancy shows up both on my device and on Garmin Connect online. So then I theorized that the system may be thinking the MaxSpeed is the slower speed (i.e., the highest pace, e.g., 9:00 minute miles), but that pretty much inverts the basic meeting of Speed.

Any thoughts or theories would be appreciated.