Problem with linked text fields

I have a fillable pdf that I have created in Acrobat XI Pro which is 4 pages long, with linked fields. I have a text field on page 3 that is formatted as a maximum of 5 characters that needs to link to a field on page 1, which is formatted the same but I have added a Custom calculation script of "event.value=getField("pg3fieldname").value", as the text field on page 1 is read only.  It works correctly until I enter in 5 zeros into the field on page 3 - then only 1 zero shows up in the linked field on page 1.

I have also done this to other text fields in the same pdf and they all work fine, except for this one.