So holds Swenson v. Bender (Minn. Ct. App. Apr. 28):
[A] fiduciary relationship cannot arise even out of a long, close, and trusting relationship when the purportedly trusting party "should have known the [other party] was representing adverse interests." Given Bender's roles as adjunct instructor at Capella and as member of the committee assigned to assess Swenson's academic paper, Swenson should have known that Bender had an independent obligation to Capella that at least paralleled, if not superseded, her obligation to Swenson as it regards the dissertation's subject matter. Bender's role prevented her from being bound to act only for Swenson's benefit on all matters.
This sounds exactly right. Bender might not have been without fault; according to a Capella University committee, she "acted unethically in her student-advisor role by developing a personal relationship with Swenson, and [the committee] found it impossible to discern which parts of Swenson's dissertation were her own work and which were Bender's." Swenson also alleged that Bender had misappropriated Swenson's intellectual property, but the trial court rejected that claim.
But that hardly says that there should be a special level of fiduciary obligation imposed on faculty members, besides the standard obligations imposed on everyone (e.g., don't steal others' stuff, don't defame them, and so on). It would be bad to conclude that dissertation advisors are primarily supposed to act in their students' interests, as opposed to the interests of maintaining scholarly standards.
And it would be especially bad to conclude, as the trial court apparently did, "that Bender's accusation of plagiarism" -- Bender had accused Swenson of committing plagiarism within Swenson's dissertation -- was itself a legally actionable breach of fiduciary duty that Bender owed to Swenson. As the court of appeals pointed out, the accusation "had merit," and is precisely the sort of thing that professors should allege when there are grounds for the allegation. And even if such an accusation were groundless, any legal remedy should be the standard defamation claim available without regard to the relationship between the parties, not some special fiduciary duty claim.
UPDATE: Whoops! I initially wrote "Swenson might not have been without fault," where I meant to say "Bender might not have been without fault"; and, on reflection, was less than clear in the rest of the discussion, too. I've revised and expanded on the material above; hope it's clearer now.