Default Dead pixel after 10 days upgraded to kitkat

Well, i have a problem with my device
it was returned from Sony Xperia Center, about 3 week ago

and i had news that sony released their kitkat upgrade for this device
so i upgrade it and so far i don't have any problem

started from Wednesday night (UTC+7), i found a dead pixel on my black color (and about 8 bright pixel) when i'm driving at night

so, my question is

• it's caused by kitkat upgrade?
• or it's caused by my tft screen? broken screen? but really it returned 3 week ago and then it got broken again (?)
• or it's caused by my tempered glass, because i never use it before, it's probably caused by tempered glass pressed too hard to my screen during installation?

thanks for your answer, hopefully Sony revolutionized the performance of their service center in Indonesia. I'm no longer have enough time for waiting my handheld on Xperia Care