Howdy K FM Fox,
I don't have FMP11, but I notice a red flag that is not FMP11 specific.
Unique ID#'s are the backbone of a relational database. Changing them allows a human to make them non-unique...this is very bad juju. They shouldn't be changed...period.
If you want a field to print a number that you make up ("227-0007" for example), create a new "Invoice #" field, put it on your layout and enter your number into that. It will print right, won't revert (unless you tell it to), and you will not risk breaking the links that rely on the unique ID#.
This is one of those "Doctor, it hurts when I do this...." Doctor: "Then don't do that" situations.
If anything, I am glad that the starter solution has a protection on the UniqueID field that prohibits you from inadvertantly messing up your relationships.