1. Create a new project
2. Switch platform to Windows Store
3. Go to Build Settings -> Player Settings -> Publishing Settings -> Misc and change the input source to Independent Input Source
4. Build for WSA Universal 8.1 SDK (.NET backend), Build type - XAML
5. Open Visual Studio solution
6. Add these lines of code to MainPage.xaml
<Grid Margin="0">
<SwapChainPanel x:Name="DXSwapChainPanel" Margin="0">
<Grid x:Name="ExtendedSplashGrid" Background="#FFFFFF ">
<Image x:Name="ExtendedSplashImage" Source="Assets/SplashScreen.png" VerticalAlignment="Center" HorizontalAlignment="Center"/>
</Grid>
</SwapChainPanel>
<TextBox x:Name="TextInputBox" Width="200" Height="60" VerticalAlignment="Center" HorizontalAlignment="Center">

</TextBox>
</Grid>
7. Deploy on local machine (Debug)
8. Observe, the native XAML component does not accept input

Expected result: Native XAML should accept input
Actual result: Native XAML component does not accept input

Note:
User has the issue only with 8.1

Reproduced with: 5.4.5f1, 5.5.2p2, 5.6.0f1, 2017.1.0a2

Workaround: make SwapChainPanel the root element of the XAML page, like so:

<SwapChainPanel x:Name="DXSwapChainPanel" Margin="0">
<Grid>
<TextBox x:Name="TextInputBox" Width="200" Height="60" VerticalAlignment="Center" HorizontalAlignment="Center" />
</Grid>
</SwapChainPanel>