qgis - Voronoi Polygon Algorithm seems to exclude a Point from processing

I am using the QGIS (2.8.1) Voronoi Polygons Algorithm on a point shapefile. See image below, the red triangles are the points I am using. The resulting polygons miss a part (around HP87).

Any ideas why?

Here is some example data (EPSG:2154) that reproduces the error (excluding point A):

X,Y,NAME
816682.58,6391443.637,A
820180.458,6391708.558,B
821325.8429,6394449.982,C
822550.1316,6397547.124,D