Symptoms
When you run a per-monitor, DPI-aware Windows Presentation Foundation (WPF) application on a high DPI setting (greater than 100 percent), the application is displayed at 100 percent DPI. This issue occurs if the target framework version of the application is earlier than 4.6.2, or if the operating system is earlier than Windows 10 Desktop Preview.
This issue also occurs in the XAML designer for UWP on Windows 8.1 applications in Visual Studio 2013 and Visual Studio 2015.
Cause
This issue occurs because of a recent regression that was introduced by the per-monitor, DPI-aware changes in WPF.
Resolution
To work around this issue, add the following element under the <runtime> section in the app.config file of your application:
<AppContextSwitchOverrides value="Switch.System.Windows.DoNotScaleForDpiChanges=false"/>
References
For more information about the Microsoft .NET Framework 4.6.2 Preview, see the .NET Framework 4.6.2 Preview known issues.