In the short time I've had my LA, I've found the same thing. Different colors of the same thread have different properties. Black is the worst offender, because they've run it through the dye vat several times. And yes, it gets frustrating. I find it is usually with the cotton threads that this happens. I don't have it so much with the polys. This is why I primarily use the Glide thread...consistency. I don't know the technical side of how they make their thread, but it's the most consistent that I've found.