Been there too
I had this happen to me shortly after Malaysia Airlines (MH) changed some fare class definitions. The plat line agent booked me, but 24hrs later it failed back. I called back and another agent informed me that the original reservation was made in the wrong (no longer correct) fare class. They continued that Malaysia Airlines rejected it, and at this moment there was no availability on any NW or ST partner flight.
I whined that from my perspective, I did nothing wrong- the mistake was NW's. The agent had put it together, I had no input or knowledge as to which class bucket they booked me in. After a few times on hold (read: supervisor calls), the plat line overrode something and confirmed me on a NW seat. I thought that was an equitable resolution.