The DPRK issued a set of 5 porcelain stamps in 1999. The KSC numbers for these stamps are KSC3983-3987. However, a careful collector might find something strange about two of the stamps in this set, KSC3983 (70 jon) and KSC 3987 (2.50 won).
These two stamps have a silver coating under the text describing the porcelain, something which the other three stamps don’t have. It is very unusual for a set to have two different designs.