Ok so a friend of mine, user ShellShocker, and I did a test battle because he suspected that Imposter copied ivs- which, according to Smogon and Bulbapedia, it shouldn't. During this test, I used a team of 6 Dittos with imposter and 2 ivs in Speed. He used a team of 6 Brelooms, with 31 ivs in Speed. We battled. This is the log. http://pokemonshowdown.com/replay/customgame10901191 So in the battle, my 2 ivs Ditto outspeed his 31 iv Breloom quite a few times- both while using priority and non priority moves. I think this is enough evidence that there is a bug.