@Lost_N_BIOS 
P67A-UD4 isn’t candidate,it’s pcie slots is the same as z68x-ud3h.So I think the mobos I mention about are the true candidate.Because the second pcie16x belongs to SouthBridge in these mobos.
I am trying to upgrade the ME FW to see whether the problem could be solved.
Edit:
Sorry for my careless expression.
what I say all of P67/Z68 had the problem is all the pcie16x belong to SouthBridge of GIGABYTE P67/Z68 had the problem.