Mine will argue with me if I try to shift too low, like others said. I've been down shifting and hit the selector left right when the car decided to downshift which threw it into first gear at way too high a speed. The rpms went up over redline and the car jerked a lot and went into neutral for a second before getting back to a higher gear. Could this be the problem, you and the car deciding to downshift at the same time?

But other than that mine has never done it. Does it actually tell you in the little indicator box that it is in neutral?