(I searched but didn't find this issue addressed)

I'm attempting to upgrade a friend traveling from RST via MSP to PHX using my One Pass miles.

RST-MSP is on Mesaba on a one-class aircraft, while MSP-PHX is mainline NW metal. Thus, I'm only interested in the MSP-PHX segment.

Speaking with a CO agent, I was told that while there are mileage upgrade seats available on MSP-PHX, the upgrade was not possible due to the Mesaba segment's presence on the reservation.

According to CO (actually the third CO agent I spoke with), this is a recognized flaw in their relationship with NW. Even though I have no interest in upgrading my friend on the Mesaba segment (it's not even possible since it's an ERJ), the Mesaba segment is preventing the mileage upgrade from being processed.

Does this sound correct to you folks? Does Mesaba not play nice with NW and CO?