I noticed a change too, but the change seems to be in terms of appearance rather than performance.
As I recall when they were first coming out they were a tad thicker all around, but they were also narrower and longer meaning they took up less space in the crotch area, but extended further to the front and back of the diaper. Now they are a tad thinner, but they are also wider taking up a majority of the crotch area left to right and shorter front to back, meaning they fit perfectly down the middle of the diaper.
It really just seems to me that they shifted some of the material around. It would be nice to have some of them from before the change on hand to see for sure. If you consult the web site though, they boast the same absorbency and I haven't noticed a significant change in performance, they still swell quite nicely and give my diapers some extra mileage. It just seems they went from a longer, narrower and slightly thicker design to a wider and slightly thinner design.