LinuxQuestions.org - Tcl/Tk Program to change Screen Resolution

Hello,

I have written a small Tcl/Tk program that changes the resolution and color depth of my X Window System. It lets me choose my favourite screen resolution and color depth and then restarts X automatically using the new XF86Config file. Now I wanted to implement a dialog box that tests the new configuration first before actually restarting X and asks the user whether that configuration is fine. I did this by opening another X session on a different console like this: XFree86 :1.0 -xf86config /xxx/XF86Config.test. Now this tests the new X configuration on a seperate X server. I can watch the black-white patterns and leave the X server by pressing <Ctrl><Alt><Backspace> and no error messages are being shown. However, I want to use a background image and a dialog that asks the user whether he wants to keep this X configuration or not. Now when I open that dialog (a small Tcl/Tk program) in the display :1.0 and press "Cancel" in order to leave the server and try a different configuration, I get an error message box (the X log file) that says (last line) "waiting for X server to shut down X connection to :1.0 broken (explicit kill or server shutdown)".
I don't understand why this error message is shown only when I use the confirmation dialog (or any other x application), and why without it, the X server will shutdown cleanly.

I am using the killall command to shutdown the X server; maybe it's too "brutal"? But then again when I kill it by <Ctrl><Alt><Backspace>, the same happens.
I know, for example, that with the other X configuration tools of other distributions like Mandrake, Suse, Redhat etc. one can get back to the initial server to test a different X configuration. But how?