Why is my wpf grid not being contained in its container?

Question

I have a user control and within it I have two controls: 1) a search criteria control (custom user control) and 2) a Telerik RadGridView.

Apart from that I have a window that is the shell for my application and in it exists three regions. When this window opens I click a button and the user control mentioned above gets inserted into one of the regions. Now that the user control is loaded I edit my search criteria and click the button to populate my grid with around 1,000 records. The problem is that the grid's scroll bar doesn't become enabled because the grid control maximizes to fit the size of all the data which runs past the screen.

The only way this works properly is to set the Height property of the grid to an absolute value but then the grid doesn't size with the window.

I've tried everything that I can think of: When in the grid I set the row def size to 200*, I put the grid in a wrap panel, I put it in a dockpanel, set the VerticalAlignment to stretch, changed the dock panel to stack panel.

Shell:

<Window x:Class="WTS.CGCApplicationInterface.CGCApplicationShellView"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"             
         xmlns:cal="http://www.codeplex.com/CompositeWPF"
         xmlns:inf="clr-namespace:WTS.CGCApplicationInterface.Infrastructure;assembly=WTSCGCApplicationInterface.Infrastructure"             
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300" Width="750" Height="480"
        Title="CGC Interface Window">       
<Grid> 
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="200*"/>            
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="Auto" />
        <ColumnDefinition />
    </Grid.ColumnDefinitions>
    <ItemsControl cal:RegionManager.RegionName="MenuRegion" Grid.Column="0" Grid.ColumnSpan="2" Grid.Row="0" />
    <ItemsControl cal:RegionManager.RegionName="SwitchboardRegion" Grid.Column="0" Grid.Row="1" />
    <ItemsControl cal:RegionManager.RegionName="MainRegion" Grid.Column="1" Grid.Row="1" />                            
</Grid>

User Control:

<UserControl x:Class="WTS.CGCApplicationInterfaceMVVM.Views.Oncor.OncorTimesheetCGC"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation"   
         xmlns:wtsControls="clr-namespace:WTS.CGCApplicationInterface.UserControls;assembly=WTSCGCApplicationInterface.Infrastructure"                  
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="600" Background="Red">     
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="200*" />
    </Grid.RowDefinitions>    

        <wtsControls:CGCQueryUserControl  Grid.Row="0"/>
        <telerik:RadGridView ItemsSource="{Binding Path=Timesheets}" AutoGenerateColumns="False" Grid.Row="1"
                                 ScrollViewer.VerticalScrollBarVisibility="Visible">
            <telerik:RadGridView.Columns>
                <telerik:GridViewToggleRowDetailsColumn></telerik:GridViewToggleRowDetailsColumn>
                <telerik:GridViewDataColumn Header="MyField1" UniqueName="AssociatedObject.MyField1" IsVisible="False" />
                <telerik:GridViewDataColumn Header="MyField2" UniqueName="AssociatedObject.MyField2" IsVisible="False" />

Answer 1

I wish I could get points for answering my own question. I do realize that this could be taken advantage of. That said, in my shell, I changed the ItemsControl region to a ContentControl and it works perfectly.