I have a new Dell T20 with the latest BIOS and am installing ESXi 5.5U3

I have installed a MegaRAID SAS 9260-8i using Cachcade on 4TB SATA's

On a power on, the T20 enumerates the MegaRAID BIOS and installs and boots ESX.

On a warm boot (CTRL&ALT&DEL or ESX restart) the T20 fails to enumerate RAID BIOS and subsequently hangs on ESX loading the mega-Raid_sas driver. Power off and on, RAID BIOS enumerates and ESX starts... 

Megaraid has latest BIOS and ESX drivers installed.

Why does T20 not enumerate RAID BIOS on all boots? is it a bug? 

HI have tried UEFI and legacy, no difference.

MegaRAID SAS 9260-8i