Similar to my previous post, we experienced another issue in result of downgrading our WPF business application from .NET 4.5 to 4.0.

The problem happens only when the application runs on Windows XP (which supports up to .NET 4.0). Although the solution is targeted to .NET 4.0 and should behave the same way no matter is the operating system version, there is a difference when you run the application on a system with .NET 4.5.

As you can see on the previous image, .NET 4.5 is an in-place upgrade to .NET 4.0, so the binaries for .NET 4.0 are replaced when 4.5 is installed.

This means our application depends on different binaries when it runs on Windows XP from newer operating systems.

Digging on the net, I discovered .NET 4.0 has a known bug around keeping synchronization context when using TaskScheduler.FromCurrentSynchronizationContext.

So in order to fix it, I adopted Steven S. solution on this thread. Basically we keep a TaskScheduler reference of the main UI thread synchronization context and use to communicate with it from long running async operations, like Task.ContinueWith methods.

This seems to fix the problem and works in both .NET 4.0 and 4.5.