X48T-DQ6, DES Advanced and flashing power on light

Just a heads up for any one else who spots this problem - when the F5
BIOS and DES Advanced are used and the Motherboard Phase LED On/Off
switch is turned on, then the power supply on LED flashes on and off
every 5 seconds or so. This had me wondering if there was some kind of
power supply or sleep state error until I was able to trace it to this
DES Advanced setting.

An undocumented "feature" (in the best Microsoft tradition) or a
fault?
***IMPORTANT***
Please do not reply to effluent@blueyonder.co.uk
This is an antispam address.
Please replace effluent with archway.