RenderWindow SetFullscreen

First of all - hey everyone, my first post and Im up to stay here longer

My problem is switching to fullscreen and back to window mode.

When i switch to fullscreen on 800x600 it does fine same resolution,
but when I try switch back to window mode with 800x600 (VS Form with FixedToolWindow FormBorderStyle) //edit
RenderWindow Height says its around 606~608 and it makes render blur.

Tried to change Form size and such...

Any ideas?

Thats my function:
private void SetFullscreen()
{
switch(Engine.window.IsFullScreen)
{
case false:
Config.Fullscreen = "Yes";
Engine.window.SetFullscreen(true, Engine.window.Width, Engine.window.Height);
break;
case true:
Config.Fullscreen = "No";
Engine.window.SetFullscreen(false, Engine.window.Width, Engine.window.Height);
break;
}
config.Save();
}


//edit//
Nevermind... switched FormBorderStyle to FixedSingle and i dont care anymore ;p