WPF: avoid redrawing of groupbox to fit content - wpf

Question

I'm using a page with a grid with 3 rows where every row contains a groupbox. The groupboxes also contain different grids with different content.
I would like to have all of my groupboxes to fit the same width. Initially that's the case. But when the content of the first group box is updated from code behind, the group box gets redrawn for a very short moment (width is smaller), but a second later it again fits to the width.
Initially it is: "not connected" which changes to "connected", so width is smaller.
The Width of my window is set to maximize, I don't want to set fix width and height for the page and the grids. Is there a way I can only update the content, without the box trying to fit to the content?
Example ( 2 rows):
<Grid Grid.IsSharedSizeScope="True" Name="globalGrid" >
<Grid.ColumnDefinitions>
<ColumnDefinition SharedSizeGroup="globalCol"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition SharedSizeGroup="RowA"/>
<RowDefinition SharedSizeGroup="RowA"/>
<RowDefinition SharedSizeGroup="RowA"/>
</Grid.RowDefinitions>
<GroupBox Header="Connection status"
Grid.Row="0" Grid.Column="0"
HorizontalAlignment="Stretch">
<Grid>
<Grid.RowDefinitions>
<RowDefinition />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<Rectangle Name="Connected"
Style="{StaticResource iconConnectStyle}"
DataContext="{Binding DeviceConnection}"
Grid.Row="0" Grid.Column="0" />
<TextBlock Text="device 1:"
Grid.Row="0" Grid.Column="1"
Style="{StaticResource statusText}"/>
<TextBlock Name="dev1" Grid.Row="0" Grid.Column="2"
Style="{StaticResource statusText}" />
</Grid>
</GroupBox>
<GroupBox Header="processing status"
Grid.Row="1" Grid.Column="0"
HorizontalAlignment="Stretch">
<StackPanel>
<TextBlock x:Name="processState" Style="{StaticResource statusText}"/>
<ProgressBar x:Name="progressState"/>
</StackPanel>
</GroupBox>
</Grid>

Answer 1

I'm now using a UniformGrid, that solved the problem...