Silverlight Grid Column widths

Silverlight Grid Column widths

I have a Silverlight 5.0 Grid with three columns, defined with widths "Auto", "*", and "Auto". Inside the second column, I have another Grid with four columns, defined with width "25*". Each of these four columns is a ComboBox.

Even though the widths are all defined the same, the ComboBoxes "Auto" size themselves, and when I select one, the box itself narrows to just larger than the down arrow, although the items are sized to fit.

<Grid>     <Grid.ColumnDefinitions>         <ColumnDefinition Width="Auto"/>         <ColumnDefinition Width="*"/>         <ColumnDefinition Width="Auto"/>     </Grid.ColumnDefinitions> <ContentControl Grid.Column="0" FontSize="20" VerticalAlignment="Center" HorizontalAlignment="Center" Margin="10,1,0,1">     <ContentPresenter Content="This is a Label" /> </ContentControl>     <Grid Grid.Column="1" HorizontalAlignment="Center">         <Grid.ColumnDefinitions>             <ColumnDefinition Width="25*"/>             <ColumnDefinition Width="25*"/>             <ColumnDefinition Width="25*"/>             <ColumnDefinition Width="25*"/>         </Grid.ColumnDefinitions>         <ComboBox Grid.Column="0" Name="comboView" FontSize="14" Margin="2,1,2,1" >             <ComboBox.Items>                 <ComboBoxItem Content="Item1" IsSelected="True" />                 <ComboBoxItem Content="Item2" />             </ComboBox.Items>         </ComboBox>         <ComboBox Grid.Column="1" Name="comboField" FontSize="14" Margin="2,1,2,1" >             <ComboBox.Items>                 <ComboBoxItem Content="Field1" IsSelected="True" />                 <ComboBoxItem Content="Field2" />             </ComboBox.Items>         </ComboBox> 

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What have I missed? When I had just one grid, with the first column set to Auto and all the rest set to something like Width=9*, the ComboBoxes did not behave this way.

After further observation, it appears that the HorizontalAlignment="Center" in the inner grid is the culprit. If I remove it, the ComboBoxes return to retaining their size, but they take up the whole outer Column 1, when I want them to take up their necessary space and then be centered within the outer Column.

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