"I have a brand new Sony VAIO S series"
This is the most important part of your question.
"What could be the cause of this strange behavior?"
Faulty hardware could be the cause. In fact, it not only could be the cause, it most probably is the cause. At any rate, it is important to go back to the first statement I quoted. This is a BRAND NEW Vaio. By any standard definition of that phrase, you have implied that the unit is still under warranty. This begs the question... why have you not contacted Sony support and arranged for the unit to be shipped back to Sony for repair or replacement for what is obviously a manufacturing defect?
It is not about your ability to repair this, regardless of what is causing the problem. This is about your ability to use the warranty that came with the unit, and get Sony to repair a problem that never should have been yours to deal with in the first place.