Incident templates Rules - On Change

Incident templates Rules - On Change

When we have a rule e.g. A Execute Script which sets the subject when a technician field is change, why when we click the edit button by the request details (Under the Requester Conversation) does the rule not fire. But when I enter the full edit mode by clicking the Edit button on the top of the form does the rule fire? Is there a work around to make this work?

Thanks

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