Responsive markup extension doesn't work with Grid succinct syntax for Row/ColumnDefinitions

[kazo0]

This works:

<Grid>
	<Grid.RowDefinitions>
		<RowDefinition Height="*"/>
		<RowDefinition Height="{utu:Responsive Wide='0', Narrow='*'}"/>
	</Grid.RowDefinitions>
	<Grid.ColumnDefinitions>
		<ColumnDefinition Width="*"/>
		<ColumnDefinition Width="{utu:Responsive Wide='*', Narrow='0'}"/>
	</Grid.ColumnDefinitions>

	...

</Grid>

This doesn't:

<Grid RowDefinitions="{utu:Responsive Wide='*, 0', Narrow='*, *'}"
	  ColumnDefinitions="{utu:Responsive Wide='*, *', Narrow='*, 0'}">

	...

</Grid>

Error:

Property or indexer 'Grid.RowDefinitions' cannot be assigned to -- it is read only
Property or indexer 'Grid.ColumnDefinitions' cannot be assigned to -- it is read only

SuccintResponsive.zip