ribbon combo box selection changed event not firing

Question

I have a combobox in a ribbon bar as follows:

<r:RibbonComboBox Label="Saved Queries" Name="Saved_Queries">
<r:RibbonGallery ScrollViewer.VerticalScrollBarVisibility="Auto"
  SelectionChanged="RibbonGallery_SelectionChanged">
<r:RibbonGallery.CategoryStyle>
<Style TargetType="{x:Type r:RibbonGalleryCategory}" 
  BasedOn="{StaticResource {x:Type r:RibbonGalleryCategory}}">
  <Setter Property="MinColumnCount" Value="1" />
  <Setter Property="MaxColumnCount" Value="1" />
  <Style.Triggers>
    <Trigger Property="Header" Value="Automatic Brush">
      <Setter Property="HeaderVisibility" Value="Collapsed" />
      <Setter Property="MinColumnCount" Value="1" />
      <Setter Property="MaxColumnCount" Value="1" />
      <Setter Property="IsSharedColumnSizeScope" Value="True" />
    </Trigger>
  </Style.Triggers>
</Style>
</r:RibbonGallery.CategoryStyle>
<r:RibbonGallery.GalleryItemTemplate>
  <DataTemplate>
    <Grid></Grid>
  </DataTemplate>
</r:RibbonGallery.GalleryItemTemplate>
<r:RibbonGalleryCategory >
</r:RibbonGalleryCategory>
</r:RibbonGallery>
</r:RibbonComboBox>

When an item is selected in the combobox, I'm trying to open a new window. But it doesn't happen. How can i go about this?