This issue occurred due to human error during assembly, it is not because the screw was overtightened.(SOM80120240)
(The cover was attached without the screw mounted through the hole on the friction plate.)
On April 17th 2015, the internal stock, which had a high possibility to have this issue was inspected(model produced in Sept.2014) .
As a result of the inspection, no issue was confirmed. Final determination is made that this issue has not occurred continuoysly.