C# Covariance+Arrays raises ArrayTypeMismatchException

Consider following generic interface ITest with a covariant type parameter T, the generic class Test implementing the interface, and a class A and with a subclass B:

 interface ITest<out T> 
 {    
   T prop{ get;}
 }
 class Test<T> : ITest<T>
 {    
     public T prop{ get {
        return default(T);    
     }}
 }
 class A {    
 }
 class B: A {    
 }

The following code compiles with errors but throws the runtime exception System.ArrayTypeMismatchException

 ITest<A>[] a = new ITest<A>[1];
 a[0] = new Test<B>(); //<-- throws exception

but this code works just fine:

 ITest<A> r = new Test<B>();
 

This has be tested on Unity3d 4.1. I already asked on StackOverflow this question. The comments suggests that this looks like a issue that is unity specific. Since the standard Mono implementation and the .Net work fine.