Andy,
Are you previewing your document in Printer Centric mode, or Optimized PostScript? The Metadata feature only works in Optimized PostScript, and if you use Printer Centric, it will not work. Make sure you use Optimized PostScript if you use Metadata.
Also, if your emulation is a User-Defined Emulation, do not use Metadata with it. The combination of User-Defined Emulation + Metadata is not supported, and may not work properly.
I would start with that. Let us know what you find!
Regards,
Raphaël Lalonde-Lefebvre