Canon has posted an advisory concerning its new EF40mm f/2.8 STM “pancake” lens. The problem is that the autofocusing function of the lens may not operate correctly if pressure is applied to the lens barrel while the lens is mounted to the camera (pressure can be applied even while attaching the lens cap or while carrying the camera with the lens attached in a bag).
A workaround is to simply detach and reattach the lens, or remove and reinsert the camera battery to restore the operations. A firmware to address this issue will be available for download in late August, 2012.
Read the advisory at: Canon.