Steps to reproduce:
1. Open attached project
2. Build UWP solution with il2cpp scripting backend
3. Open VS solution
4. Build & deploy on local machine

Actual result: Use of Windows.Foundation.Collections.PropertySet throws a NotSupportedException

Reproducible with: 5.6.2p4, 2017.1.0v3, 2017.2.0b4, 2017.3.0a1

Fixed in: 5.6.3p3, 2017.1.1p2, 2017.2.0b11

Exception thrown at 0x76B9B802 in uwp-fail.exe: Microsoft C++ exception: Il2CppExceptionWrapper at memory location 0x0A9FF750.
NotSupportedException: Cannot call method 'System.Void System.Runtime.InteropServices.WindowsRuntime.IMapToIDictionaryAdapter`2::System.Collections.Generic.IDictionary`2.Add(TKey,TValue)'. IL2CPP does not yet support calling this projected method.
at System.Runtime.InteropServices.WindowsRuntime.IMapToIDictionaryAdapter`2[TKey,TValue].System.Collections.IEnumerable.GetEnumerator () [0x00000] in <00000000000000000000000000000000>:0
at Windows.Foundation.Collections.PropertySet.get_Item (System.String key) [0x00000] in <00000000000000000000000000000000>:0
at PropertySetting.DoPropertyStuff () [0x00000] in <00000000000000000000000000000000>:0
at PropertySetting.Update () [0x00000] in <00000000000000000000000000000000>:0