Secret Ballots Anyone?

I recently heard a story on NPR (well, technically I heard it on MPR) about registered Democrats receiving a Republican Part mailing. I realize that political parties engage in all sorts of election chicanery, but this one really outraged me… and not for the reason you think.

Don’t these people complaining know that since 1892, every Presidential election in every state has been done by secret ballot? Whether they are registered as a Democrat or Republican (which I fail to see the need for anyway) is completely irrelevant. Do people believe that if the Republican party were able to switch their registration (which they’re not and which didn’t happen in this case) that they couldn’t vote for Obama?