Cannot import data into custom made Radio buttons

Steps to reproduce:

Create a new custom field.
Fill in field label
Select Data-type: Alphanumeric or Interger or Number
Select Field type: Radio
Rest leave blank.

Assign custom field to Civicrm profile

Click import and select csv file (see attachement).
Select: First row contains column headers
Make the mapping of the field(s) (saved on demo site as name "carlo")
Continiu the import

System will return with the following error: "Rows with invalid data in one or more fields"

Note: My first bug report, hope its ok.