Array.IsReadOnly inconsistent depending on interface implementation

A typed array implements both the `System.Collections.IList` and `System.Collections.Generic.ICollection<T>` interfaces, which both have their own `IsReadOnly` properties. But what on earth is going on here? ``` var array = new int[10]; Console.WriteLine(array.IsReadOnly); // prints "False" var list = (System.Collections.IList)array; Console.WriteLine(list.IsReadOnly); // prints "False" var collection = (System.Collections.Generic.ICollection<int>)array; Console.WriteLine(collection.IsReadOnly); // prints "True" ``` The `IList` view of the array behaves as I'd expect, returning the same as the array itself, however the `ICollection<T>` view of the array returns true. Is there any rational explanation for this behaviour, or is it a compiler/CLR bug? (I'd be really surprised if it's the latter as you'd imagine this would have been found before now, but it's so counter-intuitive I can't think what the explanation could be...). I'm using C#3.0/.NET 3.5 SP1.