Actually I have dozens of those Indiana Sesquincentennial stamps with FDC bullseye.
I never quite figured out how or why they did it, but the best I can guess in that someone had an "in" with the post office that prepared these cancels, as per the examples below they were trying to get the right fix on the bullseye by cancelling a blank 3x5 card, then placing the stamp over the first imprint and cancelling it a second time.
I never heard of the post office allowing such a thing, but it apparently happened as evidenced by the attached examples, which explains why there are double images of "FDOI" and only one image of the city/state/zip/date bullseye (the other is behind the stamp)!
