Yes, I believe your cursor is still in the date field. When you exit the field and commit the record the field updates to use the specified format. That leads me to believe that you are using an Insert calculated result script step. If you instead use the Set Field step, you never put the cursor into this field in the first place.
I never use the Insert steps unless I have no reasonable alternative. Set Field and Set Variable simply work better for most uses and don't have the limitations of an Insert step. (Insert steps silently fail if the referenced field is not present on the current layout.)
You nailed it. Changed to set field and it works like I want.