I've never used these, so I don't have any real ideas! Is it leaking through the PUL or out at the waist? No decent pocket should leak through the PUL. If it's leaking out the waist, does it have something to do with the design of the pocket? Can the insert wiggle out so that it touches clothes and wicks out?
I looked these up on huggabuns.com and I couldn't find a picture of the design of the diaper, but there is information there to contact the people who make them. I suggest that first!
Another random idea that may or may not help: hemp holds a ton of liquid, but it's really slow to absorb. So if your baby is a fast pee-er then a thin layer of microfiber over the hemp might help suck up the gush. Something really small like the BG newborn insert might do the trick http://www.abbyslane.com/catalog.php?category=794 I love hemp, and it's the trimmest thing I've got!
