This finally bugged me enough to do something about it - due to issues with the built-in functions for creating/updating metadata entries, I ended up writing my own set of Actions for getting, setting and deleting metadata against any vCD objects of any type. I ended up having to use the API directly as there are some definite issues in the plugin libraries for metadata manipulation.
I've attached the 3 .action files I ended up creating (set, get and delete metadata value) to this post - hopefully these will be useful to someone else out there.
Jon.
