Title says it all. So I was playing Pokémon ruby and I realized something odd. When a native Pokemon (caught in game) holds an item, it shows the default held item icon but when a traded Pokemon (charmander from fire red to be exact) holds the item, it becomes a "mail/letter" icon. What gives?
This is a "why" question that we do not know the answer to. There is a good chance that it is a glitch, but it also could be a specific action the game does to remind you that that Pokemon is a traded.
So either a glitch or a cool easter egg