I have a Satellite C50 B 15C Notebook. Part No PSCMLE 045028GR Serial 1F169667p

The screws in the back case automatically untighten themselves in ordinary operations. I saved some of them by retightening them and putting a piece of tape over the hole, so the screws don't get lost. However, I do believe that it is an error in construction and this auto-untightening should not happen.

It does multiple screws so far and my laptop is missing 6 screws so far, with others retightening or saved by tape.