Readjust neighbour-rows or Autofit Rows, when the RadRibbonview collapsed

I have an wpf application with a Ribbonview in the first row of a grid and in the second row is an calendar-control.
But when I collapse the Ribbonbar, then the second row does not follow.

What have I to change?
Here the constellation

And here : when the ribbonbar collapses, the second row does not follow

I have tried it with a stackpanel and with a grid with 2 rows..

<StackPanel >

<telerik:RadRibbonView VerticalAlignment="Top" MinimizeButtonVisibility="Visible" Height="148>


<Grid x:Name="ctlGrid_Calender_Main" Loaded="ctlGrid_Calender_Main_Loaded" Background="White" ShowGridLines="True" >