Could it be because the surface is very thin, therefore trying to "push" the pattern through from both sides? You could try using polyGroups or masking to hide the backfaces while you're painting on the outside, it might work better.
I don't think that is his problem, instead it is getting the scales to be seamless as it wraps around the object. In order to cover the object he would have to rotate it and lay down a new stroke, but he cant get them to match up seamlessly. What you could do is export the shape, and give it some new UVs. Sometimes…