Width="*" expands to fill the screen instead of the Window

[pjpmccarthy]

<telerik:GridViewDataColumn DataMemberBinding="{Binding Filename, Mode=OneWay}" MinWidth="230" Width="*" />

I have the code above and my intention is that the grid column can expand to fill the window.
However, annoyingly, what is happening is that it expands to fill the entire screen (across 2 monitors).
Is there an option/setting to fill the available space in the Window only?
(I can't imagine a scenario where anyone would want it to expand across 2 screens)