[boost] [GGL] Is this a bug, or undocumented behavior?

I have been running some of my own polygon union test cases on the union_inserter. The union_inserter doesn't appear to return a minimal set. E.g. if the start point of a polygon appears in the union, it will appear twice (consecutively). Is this expected behavior? If so, it should probably be documented. I have some other algorithms which expect a sequence of unique points, so I would need to pre-process the result of this function call. Thanks, Jon