The culprit has been busted, apprehended and charged!
I would seem that it is the flattener.
I have tested with and without on the same two objects that give issues and it is clear that when the flattener is installed I get the issue, no flattener, no problems.
The inside of the flattener is quite lightly coloured, which seems unusual. I am looking at some pot belly black paint to paint the inside before I retest it.
The flattener seems to help more with guide stars than the actual image itself, although I have not had the chance to do any long exposure tests to check the stars in the corners. Do I really need a flattener?
I will post some images later when I can get time to do something with it. I am going to image a bit with out and see what happens.
