That is no bug – it is a feature :-). If you change your exposure, shutter speed (or aperture or ISO) have to change otherwise it would be complete useless, because the combination of shutter speed, aperture and ISO is your exposure.
For your 70dFor your 70D (I tested on my 70d70D):: in manual mode you can´t change the exposure compensation. When you change the shutter speed the exposure indicator is changing.