"You said that in the Feather Step on the video clip the mans thigh is lifting the lady to a strained position. You've heard of Sir Bill Irvine. Quote In the Foxtrot he stresses on the accentuation of Third beat, this is from his Silhouette, Music and Movement Lecture given in Singapore. Could this be the lift that you think you see which is by design and not accident."
No, this is a clear and definite flaw which occurs into step 1 of the feather video, not step two (which would be beat 3). At the time of the problem, the man's knee is still quite bent - the issue is that the thigh is swinging forward too soon - the knee must not get ahead of the body until quite late in the stride. Another part of the cause is that the lady is not moving her weight back in her right foot. To review, once her feet pass her weight must be fully in her heel, then starting to move off the heel and release the toe.