Only insects have managed flight with 4 wings, the two different evolutionary chains that have managed flight in vertabrates (bats and birds) have both managed it by adaption of the forelimbs into wings. Birds dont use their legs for flying, they use them for walking, it makes no biological sense for something to use its back legs for walking, then flying, then walking again.
The example of the flying squirrel is a mammal, not a bird.

Logically I just cant see something using two sets of "wings" to fly, its evolutionary and mechanically pointlessly complicated. Sadly it's going to be a fake, or a human error, it's sad but indicative of paleontology at the moment.