MK190 out of phase

Hi, I have built two MK190 kits and both have the same problem, outputs are out of phase!?
I have checked this with oscilloscope and also by connecting headphones to output. It is clearly
heard. What is wrong, I am very confused!? A workaround is to twist terminals to one of the
spekers, but cannot be used for headphones,
And one thing more: unit stops working under 8VDC, not 6VDC as given in the manual!

Thanks for help!