AAARGH, just one of those days. All the algorithms were never designed (or tested - my bad) to work on polygons with 180 degree 'corners'. Everything from the straight skeleton to the thing that outputs faces as triangles has broken. I decided that it was inivitable that these corners would occur and there was nothing to do but fix it. I patched up the skeleton to work with the case where all edges had the same speed, but perhaps it needs a lot of futher work to work when the edges dont have the same speed.
dont have anything more to say here right now, except maybe AAAAARGH again.