Field Modification Rule not working when not all mandatory fields are filled

Config Summary:

We have a document of record date context segment which should drive the content of another DoR date context segment. For this we utilize a Field Modification Rule with auto-submit and partial page refresh.

For testing purposes we have simplified the rule, this is shown below:

Attribute 3 has the auto submit property set to true and the panel form layout is set to the ID of attribute 3 (on both new & edit flow):

Problem Description

The rule works fine when all mandatory DFF fields are filled, however if not all are filled, date attribute 4 is not updated, when date attribute 3 is changed.