Had an issue where a column converted from a text column to a dropdownlist column would display fine and update/insert fine as a text column but when converted to a dropdownlist (for the edit/insert form), the renderd 'grid' would not reflect the underlying value in the database, but would allow selection and would update the underlying database when in the edit/insert mode. Other fields converted from text to dropdown list in the same grid would behave fine. I traced this error back to the underlying column definition in the database. The misbehaving column was defined as char(10) and the working columns were varchar(10). When I converted the underlying column with the issue to varchar(10), the issue was resolved.
Just an FYI.