I noticed a few days ago that cake is eatable on everyones residences - nomatter what flags you posses. Figured someone might want to know.
I think this is because it's an item, not a block. Much like boats and minecarts (they can go in protected spawn and can be stolen from peoples residences). I don't think you can place cake in spawn though
The EMCake Party will be discussing this urgent and important issue in the very near future. Don't worry - we WILL keep your cake safe.