I have a content type with with 3 fields in addition to others, but these 3 are the subject of my issue. All fields are entity references and all fields use the Select list widget. The first two fields use "Filter by entity reference view" for Entity Selection, but the last one uses the "Simple" option. I'm not sure order matters here, but it helps to distinguish the fields. The second "Filter by entity reference view" field triggers an ajax call to update the third "Simple" field. This is the same setup as the Ajax Dependent Dropdown example in the Examples module. The ajax works fine and does what it should. However when I submit the form, I receive the "An illegal choice has been detected..." error for the first entity reference (the one not involve in the ajax transaction) and the values for that selection disappear IF I made a selection change of the second ("master") dropdown. If I don't alter that second dropdown, no problem. Any idea why this process would affect the first entity reference selection which is not involved in the ajax call?