Sebastian, the problem in this case is that startupinfo.lpAttributeList['handle_list'] contains the duplicated standard-handle values from the previous call, which were closed and are no longer valid. subprocess.Popen has always modified STARTUPINFO in place, including dwFlags, hStdInput, hStdOutput, hStdError, and wShowWindow. This update follows suit to also modify lpAttributeList in place. 

This issue is closed. Please create a new issue if you think Popen should use a deep copy of startupinfo instead, to allow callers to reuse a single STARTUPINFO instance. Or the new issue could propose only to document the existing behavior.