v1.2:if i mine only ether on my 380 card it will do 20mh, if i dual mine on intensity 30 drops to 18 mh. on 290x 28mh on eth only and 28 on dual

is it a bug or a card is weak?
and one more thing. i have 2x 380 and 1x290. the two 380 is mining on different hashrate....
My 4 identical plain 380 cards report ~ 20.7, 20.7, 20.4, and then 21.4 all at 1150/1450/-50mV 805 Watts