I've looked everywhere I might have placed coding and there is none, I have also closed down the document (having saved the changes) and closed down Acrobat and then re-opened both and the field is still showing thel ast modification date and updating that information as appropriate.
When you say "label property", do you mean the value property? What is the default value of the field set to?
Thank you very much George - I'd missed the fact that I'd set the script against the Will Save document action as well as other places.
Now deleted it and all is well.