M.I.Late

I've always called that bearding. And have had similar problems. (Used warm and natural both times - which says it's guaranteed not to beard.)
FIRST: I have one quilt with a black back - it bearded - and it is still showing batting fibers through the back - 10 years later. It did not eventually go away or anything; and It's been washed several times)
SECOND: I have a black, white and bright quilt with a black back. We kept changing needles etc. Still bearding (ripped it all out). I finally discovered that I needed to use black batting to camoflage the problem. I knew I had plenty of white on the front and didn't want to gray it out, so I basted a very lightweight white material to the top of the black batting amd it worked beautifully. Is this what you're getting?