Referenced native libraries getting pre-compiled and then throwing exception

Hi I have an issue in the universal app. I am referencing Nokia.Graphics.Imaging.dll and WindowsPreview.Media.Ocr.dll in the universal app project. Everything compiles and runs on every device I tested it with. The problem is that after some time NGen kicks in and pre-compiles my DLLs, including the native ones. These DLLs then get corrupt and next time I run the app I get BadImageFormatException due to an attempt to load the <nativelibrary>.ni.dll. Is this a bug of NGen? When I delete these <nativelibrary>.ni.dll files the app runs again.