Why does popout window resizes automatically on Safari for Windows?

Question

I created a simple html file that pop's out a window of size 310x431, but when you select/click on the pop-out window frame, you can see it getting resized (takes more width), this happens only on Safari for Windows, any reason why? or is there a way to stop it from resizing the pop-out window.

Test html file - http://dl.dropbox.com/u/3804052/pop-out.html

My version of Safari is 4.0.4 (531.21.10)