I was watching the NFLN yesterday and they were discussing the combine. Peppers came up and the discussion centered around why he was "registered" as a LB and not a safety. I believe it was Mayock, but I can't be certain, who opined that Peppers was not trying to show off his versatility, but rather mask his footwork and technique weaknesses as a DB. He felt that Peppers draft stock would plummet if he ran drills with the other DB's.
FWIW