With the registry editor navigate to:
HKEY_LOCAL_MACHINE\Software\Microsoft\Bluetooth\Au dioGateway

Look for "PowerSave" and change the value from "0" to "1". Press ok, then soft reset. Once the phone boots up and your bluetooth is recognized, make a test call then hang up. Your bluetooth should close the connection and go into standby. Make a test call TO your phone. The phone should wake up the bluetooth and route the call back through the headset.

If the PowerSave Dword is not listed, create a new Dword named "PowerSave" and set the value to "1" and soft reset, then follow the steps above.

"PowerSave" Configures audio gateway to conserve power when establishing audio connections. 
0 - Keeps the service level connection active for the Hands-Free profile in between calls.
1 - Closes the service level connection between calls.

