The children of the UniformStackPanel are not fully fit in the panel #846

<Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <hc:UniformSpacingPanel Orientation="Vertical">
            <TextBlock Text="UniformStackPanel"/>
            <TextBox/>
            <TextBox/>
        </hc:UniformSpacingPanel>
        <hc:SimpleStackPanel Grid.Column="1">
            <TextBlock Text="SimpleStackPanel"/>
            <TextBox/>
            <TextBox/>
        </hc:SimpleStackPanel>
    </Grid>