Originally Posted by Marius S
It does not say anything about the reason for having a minimum flight mass, but my guess would be that it's becuase of Vmca. The lighter the airplane, the higher the Vmca.
Since Vmca can be scheduled as a function of weight, IMHO a more likely reason is the difficulty of getting the test airplane to lower weights for certain required certification tests, considering flight test crew, instrumentation, provisions for data recording, telemetry, ballast, etc.