Since there are several (Three I think) genes that affect leg feathering quite possible clean legs on one or more grand parents. I know my hens have very sparse feathering and one none at all; bred to a male with good feathering about half the chicks came out with good feathering. I expect that even breeding them together I will still get a percentage of clean legs or nearly so for the next few generations.Convince me by showing me pure French birds with correct shank feathering throwing chicks with clean legs.
If you have correctly feathered parents throwing clean legged chicks, you gotta wonder where that's coming from, and it isn't the chicks.