What if solicitation says it is FAR Part 12 but nothing else?

I remember a GAO decision that came out years ago where the agency (I think it was the Army or the Air Force) issued a solicitation under FAR Part 12, but did not specify whether it was in conjunction with FAR 13, 14, or 15.  A vendor protested (I believe it was a post-award protest, but I may be wrong) that it was reasonable to assume that it was in conjunction with FAR Part 15.  The agency treated it as in conjunction with FAR Part 13.  The agency made missteps in the solicitation that made it unclear whether the solicitation went with FAR Par t3/14/15.  GAO sustained the protest, finding that, if the solicitation fails to specify whether the FAR Part 12 acquisition is in conjunction with FAR Part 13, 14, or 15, then it is reasonable for the potential offerors to assume that it is in conjunction with FAR Part 15.  Does anyone remember this GAO decision and what the B number was?