Parameter set to null when using editable ComboBox value

On the ribbon sample when you go to Edit->ComboBox section and type in a value that isn't listed in the drop down combo box the value will not get sent to the command. ValueCommandParameter<>.Value will be null.

A message box with "Implement text search for '' here." will be shown, when it should include the value there.

Also it doesn't seem like the change event is getting triggered all the time. For instance if you just type in "q" an tab away from the combo box the message window will not be shown.

Here is the xaml that I am tring to get working:

<ribbon:ComboBox Width="113" ImageSourceSmall="Resources/StrokeThickness.png" Label="Width:" Command="{x:Static v:SetStrokeThicknessCommand.Command}" >
<ribbon:ComboBox.Content>
<ComboBox IsEditable="True">
<ComboBoxItem>0.0</ComboBoxItem>
<ComboBoxItem>0.5</ComboBoxItem>
<ComboBoxItem IsSelected="True">1.0</ComboBoxItem>
<ComboBoxItem>1.5</ComboBoxItem>
<ComboBoxItem>2.0</ComboBoxItem>
<ComboBoxItem>3.0</ComboBoxItem>
<ComboBoxItem>5.0</ComboBoxItem>
<ComboBoxItem>10.0</ComboBoxItem>
</ComboBox>
</ribbon:ComboBox.Content>
</ribbon:ComboBox>

I've got some predefined values but want it to be overridable with any value in the textbox.

Bryan