Enable Bitlocker automatically

Hi

i have Windows 7 ENT Sp1 x86 computer and i want to active Bitlocker  during MDT 2010 deployment process

1. I've extend my AD 2003 schéma with BitLockerTPMSchemaExtension and set ACE cscript Add-TPMSelfWriteACE.vbs
2. My computer have a compatible TPM 1.2 chip and TPM is enable in the BIOS
3. I've configure GPO : Require TPM backup to ADDS and Require BitLocker backup to ADDS
4. In MDT i've enable the Bitlocker Task and the BDE partition (300mo ) is created

 When my computer is deployed, OS drive is not automatically encrypted ... i've to manually Activate Bitlocker through Explorer or launch manage-bde–on–recoverypassword C:  (and it works great)

For me, this have to be done automatically trough Bitlocker MDT sequence ... ?

Thanks for your help if i miss something ....