After installing SP1 autotuninglevel cannot be modified

OS: Vista Ultimate x86, SP1 installed over RTM.

Before installing SP1 I could modify the autotuninglevel.
After installing SP1 I am no longer able to modify the autotuninglevel.
Is seems the group policy is preventing the change.
But using gpedit.msc or rsop.msc I can find no policy that prevents
modifying this value.
Anybody else have this problem?

>netsh interface tcp set global autotuninglevel=normal

Ok.

>netsh interface tcp show global

Querying active state...

TCP Global Parameters
----------------------------------------------
Receive-Side Scaling State : disabled
Chimney Offload State : disabled
Receive Window Auto-Tuning Level : disabled
Add-On Congestion Control Provider : none
ECN Capability : disabled
RFC 1323 Timestamps : disabled
** The above autotuninglevel setting is the result of Group Policy
overriding
any local configuration.