InflatePath creates unwanted additional vertices

[ccoustet]

Hi everyone,
I stumbled on the following polygon, that when inflated, has new vertices that I cannot understand.

PathsD polyline, solution;
PointD coords[] = {
  {1427.13, 1415.78},
  {1423.51, 1416.30},
  {1419.52, 1416.89},
  {1402.45, 1419.34},
  {1403.26, 1429.07},
  {1403.63, 1433.62},
  {1421.66, 1430.96},
  {1422.90, 1430.86},
  {1423.08, 1430.76},
  {1423.88, 1438.85},
  {1429.36, 1438.44},
  {1429.45, 1438.95},
  {1441.12, 1437.52},
  {1439.33, 1414.04}
};
polyline.push_back(PathD(std::begin(coords), std::end(coords)));
std::cout << polyline[0].size() << std::endl;
std::cout << polyline[0];
std::cout << "----" << std::endl;
// offset polyline
solution = InflatePaths(polyline, -0.2, JoinType::Miter, EndType::Polygon, 2 , 6);
std::cout << solution[0].size() << std::endl;
std::cout << solution[0];
std::cout << "----" << std::endl;

14
1427.13,1415.78 , 1423.51,1416.3 , 1419.52,1416.89 , 1402.45,1419.34 , 1403.26,1429.07 , 1403.63,1433.62 , 1421.66,1430.96 , 1422.9,1430.86 , 1423.08,1430.76 , 1423.88,1438.85 , 1429.36,1438.44 , 1429.45,1438.95 , 1441.12,1437.52 , 1439.33,1414.04 
----
17
1439.15,1414.27 , 1427.16,1415.98 , 1427.16,1415.98 , 1423.54,1416.5 , 1419.55,1417.09 , 1419.55,1417.09 , 1402.66,1419.51 , 1403.46,1429.05 , 1403.46,1429.05 , 1403.81,1433.39 , 1421.64,1430.76 , 1422.84,1430.66 , 1423.25,1430.44 , 1424.06,1438.64 , 1429.53,1438.23 , 1429.61,1438.73 , 1440.91,1437.34 

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With precision=2 the resulting polygon has 14 vertices, though.