What you describe is bearding. It is more noticeable on solid dark fabrics, and some battings beard more easily than others. Warm N Natural is needlepunched through scrim, and I have to wonder if you placed the scrim side of the batting facing the top rather than facing the backing. When a batting has a scrim, you typically want to place the scrim on the opposite side from the needle entry, so you are needling in the same direction as the scrim was needlepunched. Almost any batting can beard under certain conditions. A batting with scrim will be less likely to beard if the scrim is the last thing the needle goes through.
Clear as mud, probably...... There are some informative old threads on the QB about bearding. You might want to run a search. You can also Google quilt bearding to find additional info about the problem and how you can prevent it in the future.