The different dies used for different colors effect the fabric. Some make the fabric stiffer/sturdier, some don't add much. If it seems like only one fabric had a problem, could be the die or that particular fabric was a looser weave than the others. In addition to looking at your seam allowance, take a look at your stitch length. I piece using a short stitch length to really secure the seams. As far as the batting issue, you really do need to pay attention to what it says on the package. You want to make sure that you stitch or tie within the recommended guidelines. If it says 5" (or whatever) it's 5" in all directions.