Once the cursor is in the field the second click is “INSIDE” the field not to the ‘field as a button’ object. So normal field behavior is in effect. Only by clicking out of the field or exiting the record does the ‘field object as a button’ become active again. Note that ‘tabbing’ (using return to go to the next field) can put you back into the field without triggering the Script. Unless you are using a Field Script trigger.