Originally Posted by edf825
When you hit the brakes, the momentum keeps your bike going forward. Since your center of gravity is higher than the contact point with the ground, you'll be forced forwards. This puts more weight towards the front and takes it off the back, causing the rear shock to decompress.
Seems like this is a problem that could be rectified by shifting your body position backward a bit (something that seems like a good idea regardless of brake jack). Does it really affect braking power a lot?