Frame CornerRadius Curious Behavior

I came across a curious behavior with the Frame's CornerRadius when specified with the value "0,5,0"; I pasted this accidentally and happened to notice the output below in the xaml previewer. Is this the correct behavior, and if not has it been like this for very long? The property is a float (which "0,5,0" is not and the behavior isn't documented. I can see a use for this and would like to use it but not if it is likely to get "fixed" down the road =].

<Frame Grid.Row="0" Grid.Column="2" Grid.RowSpan="2" HasShadow="false" BorderColor="Silver" 
       BackgroundColor="#FC226E" CornerRadius="0,5,0" Padding="5" Margin="0">
  <StackLayout Orientation="Vertical" Padding="0" Margin="0" Spacing="0">
    <Label VerticalOptions="Center" HorizontalOptions="Center" BackgroundColor="Transparent">OCT</Label>
    <Label VerticalOptions="Center" HorizontalOptions="Center" BackgroundColor="Transparent">1st</Label>                    
  </StackLayout>
</Frame>