Why was Roger Ross Williams interrupted on the Oscar stage?

Finally we have an explanation as to what exactly happened in that "Kanye West moment" at the Oscars Sunday night when Williams was interrupted on stage by Elinor Burkett. 

"Music By Prudence," a film about the disabled Zimbabwean singer-songwriter Prudence Mabhena, had just won the award for best documentary short film when Williams took to the stage, accepted the Oscar and began his speech. Moments later, an unidentified woman appeared beside him and interrupted his speech with her own remarks. "Let the woman talk," she blurted out.

The New York Times explains:

So what was that all about? In separate interviews at Salon.com, conducted minutes after their awkward Oscars appearance, Mr. Williams and Ms. Burkett give their sides of the story. Mr. Williams told Salon: "Only one person is allowed to accept the award. I was the director, and she was removed from the project nearly a year ago, but she was able to still qualify as a producer." Ms. Burkett said that as she approached the stage to pick up her trophy Mr. Williams "raced up there to accept the award." She added, "And his mother took her cane and blocked me."

The Los Angeles Times described it this way:

Director Roger Ross Williams rushed excitedly to accept the award and had already started his acceptance speech, saying, "I never imagined in my wildest dreams I'd be up here," when fellow filmmaker Elinor Burkett cut him off and almost pushed him away from the microphone, complaining that a man wouldn't let a woman talk. The two were whisked offstage.

The Toronto Star found humor in the moment: "Thank God for the white lady Kanye," wrote staff reporter Cathal Kelly, who described the incident as one of the few original moments in the show.

And Chicago blogger Deep Dish called it the "rudest acceptance speech."