GIGO. An IO::File object is not a valid argument. "Only" the following are acceptable:

• A file name
• A file handle
• A directory name
• A directory handle
• A typeglob reference
• A piped shell command. eq '| ls -al'
• A socket domain/port. eg 'perl.com:5678'
• '-' means STDIN or STDOUT (depending on usage)
• '=' means STDERR
• '$' means an IO::String object
• '?' means a temporary file
• A URI including: http, https, ftp and mailto
• An IO::All object

Update: Then again, passing *G or \*G doesn't work either. And neither does io->handle($h). And it's not specific to Windows.

Looks like a bug.