The most significant feature of WPF: 'Airspace fix' is NOT READY.

http://go.microsoft.com/fwlink/?LinkID=220956

2.3.9 Windows Presentation Foundation (WPF)
2.3.9.1 HwndHost redirection does not function correctly

The .NET Framework 4.5 Developer Preview includes an HwndHost redirection feature. However, this feature has several known issues.

To resolve this issue:

There is no workaround. We recommend that you do not use HwndHost redirection in this prerelease. The feature is still being evaluated and might not be included in the final release of the .NET Framework 4.5.