SATA controller on Rampage 6 extreme encore (X299 chipset)

HI everybody
In the UEFI/BIOS of the motherboard I can select the sata mode.
1 AHCI
2 Intel RST Premium (RAID)

In AHCI mode everything is working as expected (but no RAID possibility)

In the RST Premium (RAID) things are strange:

Possible to have RAID but all the sata ports are detected as being "empty".
The UEFI/BIOS "sees" the drives but the sata controller said the ports are empty. When booted in OS all the disk are well working nothing wrong.
The problem arise when I want to boot on CD/DVDROM. None of my drives plugged in the sata ports is available for boot (CSM is enabled).
Going back to AHCI mode and then all my connected sata drives can be selected to boot.
Is this a normal behavior or the UEFI/BIOS is bugged?
Thanks in advance if you can help me with that problem.
François