Most seasoned Flex coders probably know this, but as always I'm still learning. When creating a dataProvider for a List or TileList it's best to use a ArrayCollection instead of an Array.
Arrays will work if you set them as a dataProvider, but sometimes they can act weird. I just spent the last hour trying to get a TileList to update that had a Array dataProvider. Once I changed it to an ArrayCollection it worked without a problem.
So learn from my mistake. Don't use Arrays for dataProviders.