Jamie Cansdale reported a strange problem on the mailing list. His code ran successfully when run for the first time, but subsequent runs in the same process, but a different AppDomain failed with a ClassCastException.

He was kind enough to work with me to try and isolate the problem. So several hours and various private IKVM builds later, I was able to reproduce the root problem:

using System;
using System.Runtime.CompilerServices;
class Class1
{
  static void Main(string[] args)
  {
    RuntimeHelpers.GetHashCode(new Class1());
    if(AppDomain.CurrentDomain.FriendlyName != "2nd")
    {
      AppDomain dom = AppDomain.CreateDomain("2nd");
      dom.ExecuteAssembly(typeof(Class1).Assembly.Location);
    }
  }
}

This code dies with a System.MissingMethodException! Yet another weird multi-AppDomain bug.

Fortunately, the work around is easy. Instead of using RuntimeHelpers.GetHashCode() to implement System.identityHashCode(), I've gone back to using some handcoded IL in map.xml to call System.Object.GetHashCode() non-virtually. This was also what I did on v1.0 of the CLR (where RuntimeHelpers.GetHashCode() didn't yet exist).