When you have a crash, or a weird behavior, always check the player log which is located here - <user>\AppData\Local\Packages\<productname>\TempState. When submitting a bug, please include the player log as well, it can give invaluable information.
Starting from 07-12 you should be able to debug your scripts with Visual Studio. Currently it's only possible to debug C# scripts.
Here are simple steps how to do it (these steps might change in the future builds):
Go to build settings, select Type to be Visual Studio instead of AppX, you can ignore Autoconnect Profiler and Script Debugging checkoxes, on Metro they don't anything.
Open the newly created solution file. It contains Assembly-CSharp.pdb, that means you are able to debug your C# files.
The C# files are not included in this project, so you need to include them, to do so - in Solution Explorer right click on the Solution→Add→Existing Project, navigate to your Unity project and include Assembly-CSharp.csproj.
You now have all of your C# files, and you can place the breakpoints you want.
Before pressing F5, set Debug Type to Mixed (Managed and Native)
Click F5 and enjoy, you should see something like this: