Customertypecode option set includes out of the box options

1. We exported from our PROD environment those components (and all their dependencies) from the single unmanaged default solution that we required.
2. We imported that solution into our DEV environment into a completely clean, newly created CRM Organisation.
3. We noticed that for the Organisation (Account) entity the option set customertypecode includednot only the values we could see from the Customizations.xml file (obtained from unzipping (1) above)but also the OOTB values such as Competitor, Consultant, Investor etc.
4. Other option sets in other entities (e.g. casetypecode) do not include such OOTB values.

We are mystified as to how those OOTB entries have suddenly appeared!

Any ideas please?

Maz