I don't think you tested your example somehow, theres a typo in your method call extractToFileNames() should actually be extractToFileNamed().

Having modifed that, your example works perfectly fine for me on winXP, perl 5.8.8, zip.pm v1.20 - perhaps you've found some sort of regression bug. What versions are you using? And what actually happens when you attempt to extract a member twice? (Maybe paste the console output into a <code></code> block)

BTW, since your example didn't include it, are your using use strict; use warnings;