Car Radio Last-Position-Memory-Function

[Jhingo]

I encountered a very strange phenomenon: Among several USB-Sticks (all of same brand und size, all bought same day, same dealer) some do have that function (starting at the song last played after incerting car key again (like: next day) as long as stick stays in slot) others do not. I cannot find any difference in stick, tracks, file-system (fat32) or whatever. Any ideas how this can be i would appreciate very much.