Strange behavior of computed field

In my form some computed field. Values set on these computed fields by agent during clicking of button event.

In 200 document I found in one document the values in all computed fields become null means no value filed becomes blank.

How could it possible . no agent in data base which make field balnk.

Please help me how to resolve these issue

Subject: Strange behavior of computed field

MAybe you have a validation formula in your form. Or you have a document that was created with an older version of the form.