If I add a `DropShadowEffect` to an parent element the text of the child elements are blurred. Why?

```
<Grid>
    <Grid.Effect>
        <DropShadowEffect />
    </Grid.Effect>
    <Grid.ColumnDefinitions>
        <ColumnDefinition />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition />
    </Grid.RowDefinitions>
    <TextBlock Background="White">Test</TextBlock>
</Grid>

```

Update:

with shadow

![enter image description here](https://i.stack.imgur.com/UIRyJ.png)

without shadow

![enter image description here](https://i.stack.imgur.com/NNIQy.png)