It's hard to tell without more detail. For example, you haven't told us what search criteria you used in your attempt to find the records.
A few guesses:
- Radio button and check box formatting can hide data that is present in the field, that just doesn't match a value of the specified value list--someone may have changed the value list to remove a value or added a value list format to an existing field that already had data in some records... A find might find those records even thought they appear empty. You can make a copy of the field and change it's format back to "edit box" in order to inspect the fields of your found records to see if this might be the case.
- Make sure that your radio button field is not from a related table occurrence on the layout where you are performing a find. A field in a portal is almost certainly a field from a related table occurrence but other fields on the layout may also be from a related table occurrence. In Layout mode (with view sample data turned off), such a field will show :: at the start of the field name. When you put search criteria into a related record's field, you are finding records in the layout's table that have at least one related record. Once the layout returns to browse mode, however, the find criteria no longer apply and you may see data in the field from a different record that does not match your criteria or in the case of a portal, you see all related records, both the one that matched your find criteria, but all others as well.
Take a look at the field index to see the range of data currently contained in the field. Click inside the field, then choose Insert > from Index—safest to do this in Find mode. The index will show you if there is data in the field that does not match the radio buttons. If so, refer to Phil's first point.
Another thing to do is making sure that the values in the radio buttons are 100% compatible with the field definition type.