Field update doesn't work on Field edit - only works on Form edit

Field update doesn't work on Field edit - only works on Form edit

I created a Field called "TA Rep" in accounts.  I created a workflow rule to trigger on Field update....

Now, when I click the edit button that edits the entire form/record, the workflow fires and runs correctly.  However, if I click the little "edit" link for just the field and edit and save it, the workflow does not trigger.

Is this the design?