A couple of thoughts (I'm fresh from a 3 day class with Jamie Wallen and comment #1 is from what he taught us)
1. If you can see stars when you hold your quilt up to the light, and you're using no larger than an 18 needle: your tension is too tight. Do his tension test, and probably lower the upper tension. We tend to run our tension -way- tighter than we need to. KingTut is a 40wt cotton thread. It's thick, but it's easier to break than a comparable poly. I would run it as loose as I can get away with.
2. Some KingTut is crosswound, and some is stack wound. Which spool/cone do you have? If it's stack wound, it needs to unwind with the spool turning, not from the top of the spool. If it's a cone, it's probably alright on your machine. My LA dealer told me that if I check their forums that by far the most "difficult" thread to work with - based on the posts - is the KingTut. He also told me that by far the most loved thread to work with - KingTut.
3. I agree that it looks a lot like bobbin backlash on the back of the quilt. Can you load a test sammie and try with 2 different colors and do a significant amount of the same pattern? The reason I say significant is that we often quilt a little differently when we "test" than when we do an actual quilt. (I tend to be a little smoother around corners during a test than when I first start on a quilt, because I don't "care" about the test, and I don't have to think my way out of a jam. Of course if my brain would just get out of my way, I'd do a lot better all around... I digress.)