iPhone 4S problem ?

Two problems happened to me once a month. The first is when I unlock the phone and I open a SMS notification, the app is closing alone, the menu goes to the first page and the phone sleep (maybe a lag with the home button but why the phone would sleep?). When I unlock the phone the brightness is very high (note that the problem is occuring each time when i'm in a dark room...). The second problem is when I receive a SMS the sound of the sms is cut mid half and when I reply to the message the Keyboard sound is laggy but all is ok when I close the app. Others experiencing odd things like this ? The only thing I did not do is too restore as default the phone because i'm on a back up of my old 3GS.