I think the two quotes
"...Turquine so mistreated his subjects that even his personal guard abandoned him... he agreed to endure the indescribable tortures of the Fallen that he might have his revenge."
- Shade flavor
and
"The reanimated corpses of long-dead sorcerers, Shades take great pains to avoid running water (since they can only cross it by using a bridge) and act as a conduit for the evil magic of the Fallen Lords. "
-TFL manual
"The ressurected corpses of long-dead sorcerors bound to the Fallen Lords and used as conduits for their magic. "
perhaps the only power a shade has is the power to CUNDUIT other power... their natural arcane power is just the willpower to channel the Fallen Lord's power. Perhaps any strong willed person could be a shade (Like Turquine) could be a shade. Thus they have no willpower or any TRUE power on their own just the ability to channel their respective fallen lord...
well then why didn't shiver cut off the power to her shade?
note it says "BOUND to the fallen lords" the deceiver used the Binding Dream to 'rebind' it to Him instead of Shiver...
well thats my theory
"Finish me!!"
-General Pepper