I have a GA-870A-UD3 board and it does a similar thing..I am not sure but my guess is where on the board does the Motherboard
place the voltage feedback sensor..Closer to the load is the best condition..But alas that may not be practical from a layout point..One of the reasons I chose the Gigabyte board over others was the 2 ounce copper used to minimise this effect..
On my board it did not really effect anything at all that I could determine..
If someone else has more information, please feel free to jump in..
Goodluck,
jolphil