Narrow Angles still a problem

Hi apart from the previously mentioned "Cut off point for miter line joints" issue, when a polyline join gets very shallow like above it suddenly breaks the thickness and incorrectly draws the inner half of the lines and I am not sure why.

I know it is a problem if the other ends of the lines also overlap (in which case may be best to just break the joints!) but here it is still a 'where do the inner lines' cross question and then join the inner sides at that point.