I have never heard this, and even if it is possible, the odds seem extremely remote. Seat back mechanisms have been known to fail. This is usually when weighted with a heavy adult in them, during a severe rear-end crash (also very rare).
In the scenario the parent describes, there is no load on the seatback mechanism other than its own weight. It seems highly unlikely that it would fail in that mode and come forward in a frontal crash. That also assumes the seat is a fold-forward type of seat in the first place.
So, the parent would have to balance an extremely remote risk of injury to the child's legs to a much more likely injury to the child's neck and spinal cord if the child is seated front-facing.
Unfortunately, many parents get poor advice and put more faith into rumours that into sound safety practices. Pediatricians are sometimes to blame, and it's hard even for a child passenger safety technician to overcome a matter-of-fact statement from someone's own doctor that it's OK to turn a baby front facing at a young age. Other times, parents look for any possible rationalization to make it appear that safety is the factor for turning a child front-facing even though it is really one of comfort or convenience.
Although none address this parents concerns, there are a number of links to other resources on rear-facing at the bottom of our page at
http://www.car-safety.org/rearface.html .