Looks like half turn subgroup, but limited to only <=8 moves.
I like to think of it as a finish in 8 moves (reason) on a 6-color cube solved as a 3-color cube

Hmmm, http://forum.cubeman.org/?q=node/view/519 gives different numbers for >= 5 moves.
<U, D, R, L, F, B> vs <U2, D2, R2, L2, F2, B2>. See distance distribution in Phase 2 of Half-turn reduction -> Solved in my previous post (notice 13 vs 15 moves).
8 moves is quite deliberate here.
Yes, that´s because Feather´s algorithm goes like this: Any 3-color solutions that arise from the nodes being generated are then looked up in the DistP2 array (which is 3-color reduced = 4M configurations) and if it is 8 moves or less (of which there are 117K configurations) then a solution is generated.
I think the only correct number is 15 for phase 2.
I believe I covered that above.