I thought my MP rule of "metal for credit; code, forget it" broadly applied to *A, but https://www.flyertalk.com/forum/showthread.php?t=773189 indicates that EuroBonus is in fact picky about codeshares. Still, there are no flight ranges excluded on on http://www.flysas.com/en/EuroBonus/E...er/US_Airways/ or http://www.flysas.com/en/EuroBonus/E...artner/United/ , so maybe the agent was confused?

Either way, it is something peculiar to EB, and not a Star Alliance rule.