I buy Warm & Natural by the whole roll and have never had a problem with thin spots or wrinkles. I do not pre - wash either. I love the look of the little bit of shrinkage I get when washing the quilt when done.
The comment about oily spots is an interesting one. I have had 1 quilt that I made 6 years ago that developed a couple spots on only 2 of the 26 different fabrics in it. The quilt was spray-basted, probably heavier than I now spray and with a different brand than I use now. It may be because of the basting spray, it may be because of the quality of the fabric, though it was a quilt shop quality fabric, it may be the cotton batting, or a combination of all 3. The spots look a little like it mildewed a little, though I guess it could also look oily. It is a quilt I made for my DD #2 and she has it at her home so I can look at it again right now. It took several years for the spots to show. It has been washed several times and after the spots appeared I even washed it with a little bleach. I have never had any others do that, and I have made over a hundred quilts using the Warm & natural product and spray baste.
I am curious what happened and why. My boss also spray basted one and I think used W & N but used cheaper fabrics and used a whole can on only 1 queen size and she had a bunch of spots appear after a couple years also. Now, she sprayed it with a ton of spray and it took her 3 years to quilt it, therefore it was not washed until the spray had been on it for 3 years!!!