Hi there guys,
Just installed the newest version of RST.
Intel RST(e) AHCI/RAID Drivers & Software Set v14.5.2.1088 WHQL
And there's even newer one and guess what. Write-back works!
Newest is this one:
Intel RST(e) AHCI/RAID Drivers & Software Set v14.6.0.1029 WHQL
I'm gonna install it right away.
So I updated it. And it still works!