Torsten Werner discovered another but in Win32::InstallShield. Apparently ISM file tables can have null keys, so I’ve posted version 0.7 which will handle this correctly. You can grab it from CPAN or here.
I’ve posted version 0.6 of Win32::InstallShield on CPAN and here. Torsten Werner discovered that the ISM file’s encoding wasn’t obeyed and kindly offered a fix. It will now attempt to detect the encoding from the XML declaration, or allow you to set it manually.