Maybe it's loading textures so fast you can't see them all. When it says the texture it's loading, it might just be the texture it's loading at that given moment, and the system is loading them so fast it's only giving you an idea of where it is.
This would explain why some are loaded sometimes and not others. It's just displaying a different skin at different times it loads, but they're all there.
Only way to be sure is to watch it load, note something that is MISSING, have a friend spawn a plane on a runway [EDIT: I mean one that was missing from the progress screen], and spawn next to him. Look at the skin and see if it's high res or low res.