If you duplicate INVALID_HANDLE_VALUE you get a new valid handle to nothing :-) I guess the code really should not rely on this undocumented behavior. The reason I didn't return INVALID_HANDLE_VALUE directly is because DuplicateHandle returns a _subprocess_handle object, not an int. It's expected to have a .Close() method elsewhere in the code.

Because of subtle difference between in the behavior of the _subprocess and win32api implementations of GetStdHandle in this case solving this issue this gets quite messy!
File Added: subprocess-noconsole2.patch