Fields not autofilling

I'm sure I'm missing something simple here.

when creating a Prod Order from a Sales order, the Gen Bus Posting Group & Location (both have only a single option available) fill automatically.  However, if I create a Prod Order from scratch, those fields don't autofill.  Is there a way to do this automatically or is it because the info for those fields is pulled from the Sales order and can't be done automatically otherwise?

Using NAV 2009 (SP2)

Thanks.