Datagrid height not decreasing beyond number of visible rows.

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WPF

Hi,
I am using a Datagrid. The grid initially has 7 rows. Dynamically when I add more rows datagrid behaves normally and adds scroll bar if rows grow beyond the specified size.
I increase the size of window the grid expands and now when I try to reduce the size of window the problem occurs. The datagrid shrinks only until all the rows are visible.
Ideally if I try to reduce the size of window, datagrid size should decrease and the scrollbar should appear, but this is not happening.
Below is the code. Datagrid is inside a grid which is futher in a grid and this page is viewed in a frame on some other window.
Please suggest.

<pre> <grid grid.row="2" grid.column="0" margin="0,3,3,0" name="gridLogTableHolder" sizechanged="gridLogTableHolder_SizeChanged">
            <grid.rowdefinitions>
                <rowdefinition height="auto" />
                <rowdefinition height="2*" />
            </grid.rowdefinitions>
            <grid grid.row="0" removed="White">
                <grid.columndefinitions>
                    <columndefinition width="{Binding ElementName=colColor, Path=ActualWidth}" />
                    <columndefinition width="{Binding ElementName=colMx, Path=ActualWidth}" />
                    <columndefinition width="{Binding ElementName=colMy, Path=ActualWidth}" />
                    <columndefinition width="{Binding ElementName=colML, Path=ActualWidth}" />
                    <columndefinition width="{Binding ElementName=colMDE, Path=ActualWidth}" />
                    <columndefinition width="{Binding ElementName=colRx, Path=ActualWidth}" />
                    <columndefinition width="{Binding ElementName=colRy, Path=ActualWidth}" />
                    <columndefinition width="{Binding ElementName=colRL, Path=ActualWidth}" />
                </grid.columndefinitions>
                <border grid.column="1" grid.columnspan="4" borderbrush="Black" horizontalalignment="Stretch" borderthickness="1">
                    &lt;Label Content="Measured" HorizontalAlignment="Center" Foreground="Black"&gt;&lt;/Label&gt;
                </border>
                <border grid.column="5" grid.columnspan="3" borderbrush="Black" horizontalalignment="Stretch" borderthickness="1">
                    &lt;Label Content="Reference" HorizontalAlignment="Center" Foreground="Black"&gt;&lt;/Label&gt;
                </border>
            </grid>
            <datagrid grid.row="1" autogeneratecolumns="False" horizontalalignment="Stretch" verticalalignment="Stretch" name="logTableGrid" headersvisibility="All">
                  HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto" MouseDoubleClick="gridElement_MouseDoubleClick" AlternatingRowBackground="AliceBlue" Rowremoved="White" IsReadOnly="True"&gt;
                <datagrid.columns>
                    <datagridtextcolumn header="Color" binding="{Binding Key}" x:name="colColor" width="*" canusersort="False" xmlns:x="#unknown"></datagridtextcolumn>
                    <datagridtextcolumn header="x" binding="{Binding Measuredx,StringFormat={}{0:n3}}" x:name="colMx" width="*" canusersort="False" xmlns:x="#unknown"></datagridtextcolumn>
                    <datagridtextcolumn header="y" binding="{Binding Measuredy,StringFormat={}{0:n3}}" x:name="colMy" width="*" canusersort="False" xmlns:x="#unknown"></datagridtextcolumn>
                    <datagridtextcolumn header="L" binding="{Binding MeasuredL,StringFormat={}{0:n3}}" x:name="colML" width="*" canusersort="False" xmlns:x="#unknown"></datagridtextcolumn>
                    <datagridtextcolumn header="DeltaE" binding="{Binding MeasuredDeltaE,StringFormat={}{0:n3}}" x:name="colMDE" width="*" canusersort="False" xmlns:x="#unknown"></datagridtextcolumn>
                    <datagridtextcolumn header="x" binding="{Binding Referencex,StringFormat={}{0:n3}}" x:name="colRx" width="*" canusersort="False" xmlns:x="#unknown"></datagridtextcolumn>
                    <datagridtextcolumn header="y" binding="{Binding Referencey,StringFormat={}{0:n3}}" x:name="colRy" width="*" canusersort="False" xmlns:x="#unknown"></datagridtextcolumn>
                    <datagridtextcolumn header="L" binding="{Binding ReferenceL,StringFormat={}{0:n3}}" x:name="colRL" width="*" canusersort="False" xmlns:x="#unknown"></datagridtextcolumn>
                </datagrid.columns>
            </datagrid>
        </grid

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