This has already been discussed, and it's an optimization that FSX does to save fps, it will disable all animations after a certain visual distance, if you zoom a bit, the animation will show.
You can also set the SmallPartRejectRadius tweak to 1, but this might affect the fps a bit (if you raised it), so it's probably best to simply not use a too wide zoom setting.
Good to know, however the reason I asked is due to the fact that I keep my zoom in the VC always at .80 and the wing walker is always the same distance from the vc at the same zoom factor. Plus the fact that with the zoom level being the same, I can depart one airport and the legs work fine and then when I depart my next airport the legs will freeze up. I supose that the reason could be it at the airport where the legs are frozen it could just be that the said airport is harder on performance, hence the legs freeze up. It rarely happens and I have even flown trips consisting of 5 or 6 legs the in the same FSX session without exiting the sim and it never happens, while when it happened yesterday it was when I was starting push back at the second airport I was departing.
Thanks for the info Umberto and at least I know its not a bug and is in fact just due to how FSX handles certain situations.