This is an old database, but a new problem. Updating a field in the form loads a new primary key to the form. That makes it appear that the update will go to the wrong record. Closing the form and opening it again makes this problem disappear for a while. The form is on a networked computer and the back end is on a SBS2003 on the same local network.
Any idea what is going on? To me the answer is just one thing; Microsoft.