Apparently, I am not alone in having a missing opportunity to take good picture because of the undesirable changes in shooting mode due to inadvertent knocking of the dial mechanism of the EOS Canon camera. For example, after carefully setting the shooting mode to capture a portrait with a nice, wide aperture and released the shutter only to find that you are waiting for a 2-second exposure to finish up. Or capturing a decisive moment of street action, only to find that your Shooting Mode dial is in green-rectangle-full-Auto mode or Tv Mode (Shutter Speed Priority).
Apparently, there are a lot of users having similar problems and for EOS 5D Mark II and EOS 7D users, Canon provides a chargeable service to install a brand new, lockable, press-and-turn mode dial.
Unfortunately, the service is only available in USA, what a pity.
However, for the time being, I have to keep on double checking the dial mode before taking pictures in order to ensure the right setting is being used.
For further detail, click HERE.