I'm going to reopen this ... now I'm getting the same crash for a different event - OnPointerMoved ...
Exception at 0x75864192 in Demo.exe: Microsoft C++ exception: EEFileLoadException at memory location 0x12DDD0EC.
Exception at 0x75864192 in Demo.exe: Microsoft C++ exception: [rethrow] at memory location 0x00000000.
Exception at 0x75864192 (KernelBase.dll) in Demo.exe: WinRT originate error - 0x80131040 : 'System.IO.FileLoadException: Could not load file or assembly 'System.Runtime.WindowsRuntime, Version=4.0.15.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040) at Engine.Interaction.MouseEventProcessor.OnPointerMoved(Object sender, PointerEventArgs e)'.
I noticed that the app that works has my engine code dragged over to the project, while the two apps that crash are using a library. I'm going to setup two identical projects with just this difference to test.
The page wouldn't let me say this as a comment - these forums are really bad.