Migration problems with EntityFramework 7 and Data Annotations

I’m currently developing a new UWP app for Windows 10. A chance to try the new EntityFramewok 7 (RC2) with SQLite. 😉 Although it is still not final, it works very well. But there are still some strange things. I figured out a problem with the [NotMapped] Data Annotation. At some point I wasn’t able to create migrations anymore.