window size always changes after restart in 10.9.2. How can I fix it- as in older OS-Versions?

Hi,

I'm using OSX for a long time. Now I bought a new MBA 10' with Mavericks 10.9.2. I'm really tired about ever changing window sizes after restarting my MBA, espacialy the sidebar is skipping to a wider size, then the window, I used before turning the mac of. No window opens, in exact that size I used before. Of course, I used to fix it, but never menaged to do so.

Have you any idea to solve my problem?