Mass Update error

We were running a mass update after a change to both a label and field name. A view was created to select all the records with the old field name and label, and this was used in the mass update procedure. When executing the procedure, we got an error to fill in a different required field, and the update did not transpire. This required field had no relation to the field we were updating, other than being in the same object and form. After some trial and error, we got the update to work by making the required field required at field level only, and not at the form level.

Our question is, why did our solution work?