Thanks for replies, mean and Jan!
Window manager? As far as the OS Windows is referred (my case; Win7, x64),
each program's main window must have an x-y pos, width and height as properties: by that the starting pos is defined.
Normally, if you intend to screen-center a form, you have additional work to do yourself _manually_, somehting like
this.Location = new Point((Screen.PrimaryScreen.WorkingArea.Width - this.Width) / 2,
(Screen.PrimaryScreen.WorkingArea.Height - this.Height) / 2);
OR you have some macro for the windows style available, provided by the compiler, something like
this.StartPosition = FormStartPosition.CenterScreen;
The normal case should be to use the x, y - position property and have not align macro or style definition.
I guess, in windows coding you use something like that behind the scenes.
I would vote not to use screen alignment of the main window but x, y pos and save them as pref.
That had never been a problem for me until i noticed cases where the ADM main windows was resized by contents
and parts of the main window now are truncated by the screen boundary (parts become invisible).