I think I've found a workaround. The problem seems to be that I don't know how to use a ListBox properly. I see that Rick has a Developer Lesson on this. If my current scheme works, I'll wait patiently until I get to that lesson in normal rotation.
Temp solution: I deleted the ListBox and placed a more familiar ComboBox in its stead. Reading its RowSource from a dedicated table with 2 fields, an "ID" autonumber and "NameString", I can use the ComboBox's "After Update" event to place code that inserts Me.ComboBox.Column(1) in the TextBox. I think I can bind the Combo to the Form's Table "thing" field (and not the TextBox) and preserve the value, leaving the TextBox to be properly updated via subroutine when later returning the Form to the same record.