During his trail hike experiencing NZ weather, he agreed. Joe's theory was the water was entering from the top sewing seam of the zipper. On returning to the US, Joe tinkered with some new designs. He came up with a simple solution that works well.
Not only are these new pockets waterproof (Joe tested them in the shower!), but much easier to use. I always found the zippers a bug to open and close as they sat on a horizontal plane.
These are not on his website yet, but if you are interested, I am sure Joe will make these for you. To explain - these are like a tube with an elastic opening, much like side pack pockets. To close, you just fold over and clip shut.
Here are a couple of pictures.