Product and version: FileMaker Pro 16.0.2
OS and version: macOS Sierra
Hardware: MacBook Pro, early 2015
Description: On a layout, once a field has been associated with any value list, there is no way of disassociating it completely from all value lists - the only option is to change the value list with which it is associated. In other words, once a field has been associated with any value list it must be associated with some value list - there is no way to return it to the original state of not being associated with any value list.
How to replicate: Create a drop-down field. By default, it is not associated with any value list. Select a value list to provide the values. Now try to remove all references to value list to return it to its default state. (You can't.) Duplicate the field and change it to an Edit box control style. A value list is no longer needed, however FileMaker continues to store the value list reference from the original field (pulls up in the DDR). You can change it back to Drop-down list control style to see the associated value list, but there is no way to remove that reference to the value list even though you now intend to use the field as an Edit box.
Workaround (if any): When I come across a field that is now an Edit box but was duplicated from a field with a reference to a value list, I either change the value list reference to a dummy, blank value list so that I don't get false references in the DDR or I delete the layout object and re-create it as an Edit box with no value list reference.