Just from my experiences, I've noticed players disappearing from scout list so I don't think it's unique.

What does annoy me though is if you buy a player from the list there seems a good chance that another better quality player appears to replace him on the list straight away. This happened to me with a GK a few days ago. But this doesn't seem to happen if someone else buys a player, they just vanish and are not replaced on my list.