Update Document Choice Field half way works!

I'm trying to update a choice field. I can get the field to update, but when I go look at the metadata of my document it's as if the field isn't really updated. It's like it's updated in text only. Once I try to edit the field is empty.

Function GetChoice($field,$lookup){


    $lookupfield = $item.Fields[$field].GetFieldValue($lookup)

      return , $choicevalues

}

David Jenkins