Any flat finish can get the shiny spots if something oily gets on it. While sanding the clear achieves the "look", you have actually opened up the finish and can make it more prone to the dreaded spot. In can be cleaned though, think of it from a car painters (me) standpoint. The last thing I do before paint on a sanded (flat) finish is to de-grease it. No shiny spots what so ever. Invest a little in some final wipe, not a regular wax and grease remover (DX394 works great) and use that to clean the finish when needed.

Dan