AdvancedCustomFields/acf5-beta — pull request #245 by gmcmicken (2014-05-26 19:16:26+00:00)
Title: "Select" field to include orphaned values

If a user re-defines "Choices" for a "Select" field, any previously
selected items which are not part of the new choice list would be hidden
and un-selectable. Changed behaviour to add "orphaned" items to the
select menu first in the list and marked selected.