yes, I know that BTC/mhash is for accepted Mhash not total Mhash, thats why hinted on mining with same rig on different pools
as for high duplicate shares reject rate, this usually is client side issue with multiple gpu's running in same cgminer instance (and something broke there).
Another explainantion would be really badly broken stratum, but as it seems most the other users do not have this issue I think its client on side.
cgminer debug log could show more...