Nissan Note rear window screen smashed

I brought the car in march 2009 there has only been myself and the nissan dealers whom have owned this veichle. Last wednesday i had a phone call from my parents saying the back window screen had smashed. It had not been broken into as my mum was cleaning her car at the time it happened. The window cracked from the left handside to the right hand side of the window except the bottom half of the smashed window was shattered but the top half remained ok untill my brother opened the boot to have a closer look. I had not been in the car since the morning of the monday and it smashed on the wednesday late afternoon. I was wondering if anyone else had any problems with theres.