ProjectToCPlane Bug - Extrusions

ProjectToCPlane result with closed extrusion (box) is strange and not as expected. Result after ConvertExtrusion to polysurface is as expected. (6.0.18002.10461, 1/2/2018)
ProjectToCPlaneBug01.3dm (53.9 KB)

Hi David - I see that… weird. Thanks.
https://mcneel.myjetbrains.com/youtrack/issue/RH-43355
-Pascal