You don't mention where this is happening (e.g., directly in the table, via
a form, ...)
I've seen similar behavior if a datasheet view was used. If that's your
situation, consider using a continuous form and creating a single record's
controls in that form. That way, the combobox only applies to that record.
And as other responders have pointed out, leaving a control unbound tells
Access that it applies to ALL records that control appears with on the form.
Of course, since it was unbound, the underlying table will NOT reflect the
choice! Does your table show the change in all records, or is this just
appearing to happen in a form?
Regards
Jeff Boyce
Microsoft Office/Access MVP