How can I make transitions honor UseLayoutRounding?

Question

I have a page in my C#/XAML Metro app that animates in using EntranceThemeTransition. Inside this page, I have some tiled graphics: Images that fit snugly against each other to build up a larger image. I made sure to make the sizes multiples of 5, so they'd fit nicely even at different DPIs.

Since the default value of UseLayoutRounding is true, I expect every step of the EntranceThemeAnimation to be rounded to the nearest pixel. However, this isn't happening, as this screenshot shows (notice the two thin green vertical lines through what's supposed to be a solid block):

This is supposed to be a seamless block, made up of 9 tiles (3 wide x 3 high, each tile 80x80 pixels). Vertically, they fit together perfectly; but while the page is animating in, because the X direction is being animated and isn't always a multiple of 1 pixel, I end up with seams between the tiles (since each image's X is fractional, so you've got two images each drawing the middle pixel with 50% opacity on top of what's already there, resulting in a total of 75% opacity instead of 100%). This is the very sort of problem that UseLayoutRounding is supposed to prevent, but it's not helping at all.

Once the animation is done, then everything settles in and things line up perfectly. But during the animation, and especially right before the animation stops, the seams are pretty noticeable.

I tried explicitly setting UseLayoutRounding="true" at various points in the parenting hierarchy, but it didn't help.

Here's a simplified form of my XAML that reproduces the problem:

<Page x:Class="App1.Page1"
      UseLayoutRounding="True"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Grid Background="Green" UseLayoutRounding="True">
        <Grid.ChildrenTransitions>
            <TransitionCollection>
                <EntranceThemeTransition/>
            </TransitionCollection>
        </Grid.ChildrenTransitions>
        <Canvas UseLayoutRounding="True">
            <Image Canvas.Left="80" Canvas.Top="80" Source="/Assets/DirtSquare.png" Width="80" Height="80" UseLayoutRounding="True"/>
            <Image Canvas.Left="160" Canvas.Top="80" Source="/Assets/DirtSquare.png" Width="80" Height="80" UseLayoutRounding="True"/>
            <Image Canvas.Left="240" Canvas.Top="80" Source="/Assets/DirtSquare.png" Width="80" Height="80" UseLayoutRounding="True"/>
            <Image Canvas.Left="80" Canvas.Top="160" Source="/Assets/DirtSquare.png" Width="80" Height="80" UseLayoutRounding="True"/>
            <Image Canvas.Left="160" Canvas.Top="160" Source="/Assets/DirtSquare.png" Width="80" Height="80" UseLayoutRounding="True"/>
            <Image Canvas.Left="240" Canvas.Top="160" Source="/Assets/DirtSquare.png" Width="80" Height="80" UseLayoutRounding="True"/>
            <Image Canvas.Left="80" Canvas.Top="240" Source="/Assets/DirtSquare.png" Width="80" Height="80" UseLayoutRounding="True"/>
            <Image Canvas.Left="160" Canvas.Top="240" Source="/Assets/DirtSquare.png" Width="80" Height="80" UseLayoutRounding="True"/>
            <Image Canvas.Left="240" Canvas.Top="240" Source="/Assets/DirtSquare.png" Width="80" Height="80" UseLayoutRounding="True"/>
        </Canvas>
    </Grid>
</Page>

What can I do to get the layout to actually round all the positions to the nearest pixel, even while the EntranceThemeTransition is animating the page in?