It's a bug in the control as I thought. Check out what Microsoft says about it:
BUG: The Margin Value Decreases Every Time PageSetupDialog Is Displayed
http://support.microsoft.com/?id=814355
"Amjad" wrote:
[color=blue]
> I use the PageSetupDialog box to allow the user to change the page margins
> before printing. The problem is when I open the dialog box and type in margin
> values in millimeters (as it says in the group border title), click on the OK
> button, and then open the dialog box again, I find that all the margin values
> were divided by 2.54.
>
> Basically, every time I open that Dialog box and click on OK, all the margin
> values get divided by 2.54.
>
> I know that this is a metric-imperial unit problem, but I don't know how to
> fix it. I have used the following code to open the dialog box:
>
> Dim pd As PrintDocument = C1grd.PrintParameters.PrintDocument()
> PageSetupDialog.Document = pd
> If PageSetupDialog.ShowDialog = DialogResult.OK Then
> MsgBox (PageSetupDialog.PageSettings.Margins)
> End If
>
> Any help is appreciated[/color]