It's the tight weave and high thread count of really nice cotton sheets that give long-armers fits, especially when densely quilting. For this purpose, cheaper is better. Think the nasty coarse sheets in cheap motels, camp, and the Army - perfect for quilt backs, if new and washed once.
Put a microfiber polyester sheet on the back of a quilt and it will slide right off the bed the second the cat jumps on it.