I don't have my 40D in front of me, but when you access flash control in the camera menu, what are the "built-in flash settings"? If it's set to E-TTL, it will change the power to expose properly.
Let us know!
Adrian
I've had to start over after changing my password and not being able to access forums after logging in. I'll still try to get that account back, but I have started all over again with a new account.