Metro App, no graphics refresh after resume

I'm developing a Metro Windows Store App (Win8.1) with Unity3d. The Problem is that after the App was suspended and resumed the App no longer refreshes the graphic output from Unity but Unity still get Update calls and handles Input. Even the XAML Gui elements (like textboxes) work but neighter Unity GUI nor Camera output is drawn. The App looks like its freezed.

I am building a Unity C# XAML Solution with 8.1 Sdk.

Does anybody encountered similar problems on Win8.1 Metro App Builds?

May it be an Unity3d Engine Problem or can i do something on my own to reconnect Unity to the DX Output after App resuming?

I' m still connecting to the suspend and resume Events as Microsoft states, that not handling it in a timespam of 5sec will terminate the App... But this had no impact.

I am grateful for every tip...