I am having a similar issue. I have a select field with 60 or so values (with separate labels / values). When I add in a new value in the select field, and go to a page that already has a value set in the select field, it shows as blank (the first option in the select box). At this point, in the Database it is still correct. Once I click Update/Publish, it then incorrectly changes it to the first value/blank value.