The play:
http://www.youtube.com/watch?v=qSqRgzjl2m8
Penalty was enforced from previous spot. Appears crew got 2 different fouls and penalties confused and the enforcement reflected a "blend", i.e. 1 certain foul but with the enforcement that is mandated for the other foul.
If the determination was that the ball or other players were interfered with, then the R can enforce any penalty he deems equitable. If he thinks it is equitable to enforce from prev spot. 1/2 the distance, but no replay of down, so be it. I do not think that is what he was doing though.