I created the custom shape PCB and was able to open it in Fritzing. It looks ok. I can export as a JPG . Looks perfect. But when I export it as etchable PCB I see the inconsistency in the shape. Any idea why?
What fritzing version are you using (some of the older ones have a problem like this.) It would also be a good bet to upload the outline svg (upload is the 7th icon from the left in the reply menu) so we can try it and see what happens for us (and look over the svg which has some format requirements.)
Peter