In fact, Harvard Law School was actively (almost monomaniacally) on the hunt for a more "diverse" faculty during the early- to mid-nineties. It was part of the aftershock of the Derrick Bell resignation and controversy over law school hiring practices -- diversity was a big, big, major deal. Designating oneself a Native American was almost surely a significant point in one's favor at Harvard Law School in the mid-nineties -- even more than ever before or after -- if the goal was to obtain a coveted tenured professorship there.
So when it turns out that Professor Warren has claimed a significant competitive benefit -- and then can't even readily document the source of that claim -- there's sure to be a controversy. That's especially true if, as her spokesman claims, she's "proud" of her heritage: Why, then, did she drop all references to it after gaining her Harvard post?
Finally, the very concept of looking at race or ethnic heritage to advantage some (at the expense of others) in higher education is already controversial. To the extent that many people can justify it at all, in their own minds it's a potential remedy (or at least some kind of compensation) for the injustices readily identifiable members of certain minority groups may confront in certain situations. It's clear that Professor Warren -- blond, blue-eyed -- never confronted any disadvantages because of her Native American heritage . . . so perhaps Massachusetts voters are wondering why she should have felt herself entitled to claim special benefits arising from it.