A typed array implements both the System.Collections.IList and System.Collections.Generic.ICollection 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)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 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.