someone else mentioned it, but i've had it happen to me personally. (i was the guy landing) just because someone doesn't think they are going to land doesn't mean they won't be coming down soon, and some planes glide like rocks... I had my shrike deadstick on me once with someone on the runway, and from deadstick to on the ground is about 5 seconds. they managed to move VERY quickly to get out of the way of a very fast moving shrike, but had i not been sure they had been out of the way i would have been forced to ditch a plane to avoid someone on the runway.

personally i would not do that with anyone in the air, beyond that I think it is fine.