not sure if special tickets and Cat Cs are in the same available category. It appears so, or some kind of matrix where when a special ticket is purchased, it reduces Cat C's available...
There is a big problem with Korean cabin crew buying the special tickets and flipping them to people who are not their friends for a quick scalp.
If you want to get home, just figure out the "Korean black market" and buy your staff travel tickets from them.
I remember a while back an e-mail warning people, but its still happening, screwing everybody.