Not sure where from.
It almost seems like it's coming through the PUL at the front, but surely not? These are the one-sizes - I tried those and the size 1s in a nappy trial and found the size 1s leaked st the waistband, so went with the one-size. I have them poppered down and it was particularly wet in the fold of the poppered down bit. Could it be wicking round from the legs?? I suspect you don't get as good a fit round thighs when they're poppered down. Also, DS2's legs could be chunkier!
It's a shame, as they're so expensive. I'm new to cloth and after trying a local council bucket trial, bought a clutch of assorted nappies second-hand from local sellers and ebay. I'm having a lot of fun with them! 
The pop'n'gros were 2nd hand too, but were basically brand new - bought from a seller on ebay along with some all-in-one pocket Tots Bots, and she'd hardly used them at all - the velcro was pristine and there was zero bobbling, so I believe her!
Any thoughts? Is this happening to anyone else?