Recall that there was some movement artifact in the tympanogram tracings.  This is also seen when testing reflex decay.  The contralateral 500Hz trace is what is typically seen for a cooperative patient; the others show artifact.  By observing the size of the initial deflection and the size of the reflex at the end of the 10 second period, as the muscle contraction ends and the trace returns to baseline, you can see that the reflex has not substantially decayed.