I have never known W&N to beard. The wrong side up doesn't really result in a bearding issue (wispy threads of the batting coming through the quilt top or backing fabric) but little blobs of the bat being pushed through the needle hole. I call them pokies, but I also call the spots of thread that sometimes migrate if tension isn't just right pokies. Used to be wool and polyesters battings were nortorious for bearding. Is it possible the natural batting you are using is wool?
Most needle punch battings don't beard and better quality polyesters and wools are resin bonded to resist fiber migration. However, that doesn't make it foolproof. If you went with a traditional cotton that doesn't have scrim or needlepunched like say, Mountain Mist Blue Ribbon, then I suspect there could be fiber migration. Not sure if it will run its course with washings or not. Sometimes they do, sometimes they don't. As an aside, a quick internet search uncovered this review that talks about the problem being more common with solids. this particular quilter was using Quilters Dream poly. I too have used this batting in black and did have some bearding while hand quilting but it seemed to resolve itselt after washing.
http://dreamweavers-quilts.com/2008/...atting-review/