First node floats to top left corner

I’ve started a new WPF based project using GoXam and am seeing some unexpected behavior: when I start with an empty diagram and drag the first node onto it, that node floats from the drop location to the top left corner. All subsequent drop operations position nodes where I expect them. I suspect there’s just some view property of which I’m not aware. How can I get the initial node to be positioned at the location where I ended the drag/drop operation?

I’m using a GraphLinksModel that simply creates a new GraphLinksNodeModel derived class (which is currently empty), sets the location to the of the node model to the drop point, and adds it to the model.

Here’s my pretty simple XAML. I’ve omitted the view model which acts as the data context and publishes the model for the view as well as the Blend behavior that shuffles the drag/drop data eventually around to the model. As I said, this all works as expected except for the initial node.

  <DataTemplate x:Key="NodeTemplate">
    <go:NodePanel go:Node.Location="{Binding Data.Location, Mode=TwoWay}"
      <Rectangle Width="20" Height="20" Fill="Azure" />
    <RowDefinition Height="Auto" />
    <RowDefinition Height="*" />
  <go:Diagram Grid.Row="1"
              Model="{Binding Model}"
              NodeTemplate="{StaticResource NodeTemplate}">

Set Diagram attributes HorizontalContentAlignment=“Stretch” and VerticalContentAlignment=“Stretch”

Thanks, that fixed it.