i am not sure about the ruling:
In general when you use the SP-field you can chose to either take SP AND/OR build a minor. You cannot take the action if you decide to perform neither of the actions. So far so good and so correct.
But now, what in rd 14. I can chose to take SP without building a minor (blocking the field). I am not sure whether taking SP is an allowed action in rd 14. My feeling tells me it's not, but my feeling has nothing to do with the correct ruling.