Perishable hats placed on a waxed Snowman will still spoil, despite being waxed.

If you put something like a fashion melon or garland on a snowman, then wax the snowman, its hat will still spoil after a few days, even though the snowman is waxed and thus by the game's rules should stop the hat from spoiling. This stops you from using those hats as decor, even in places where it would fit perfectly (like a pirate monkey snowman with a banana peel on its head!).