We learn in Season 5 that Jack bought a pair of brand new white tennis shoes to put on Christians' corpse before flight 815.
He did this because, at the time, he didn't believe that his father was 'worth' the cost of nice shoes to be buried in. Now, can we all agree that the white tennis shoes were worn by Christian? And can we further agree that the same brand new white tennis shoe, hanging by the laces as Jack exits the jungle in Pilot, part 1, were in fact, worn by Christian as well?
As long as we agree, I find it odd that the shoe found in the tree (at the beach) is a significant distance away from the closed coffin and Christians' corpse (in the caves). The distance between the caves and the beach is approximately one mile.
Furthermore, the coffin was closed and laying nearby the Oceanic cargo compartment. If the coffin (and hence the shoes) were locked into the cargo compartment, then why would the shoes be hanging from a tree one mile away?
Yes, I totally understand your concern. Although, if some of you agree, I would feel more than happy to discuss.