The current implementation allows continuing the enumeration of an enumerator after its disposal:

// Prints: True42 disposed True43
// Expected: True42 disposed False42

var enumerator = C.GetEnumerator();

System.Console.Write(enumerator.MoveNext());
System.Console.Write(enumerator.Current);

enumerator.Dispose();
System.Console.Write(" disposed ");

System.Console.Write(enumerator.MoveNext());
System.Console.Write(enumerator.Current);

class C
{

    public static System.Collections.Generic.IEnumerator<int> GetEnumerator()
    {
        yield return 42;
        yield return 43;
    }
}

According to Spec for MoveNext and Dispose for enumerators, MoveNext should return false after disposal:

The precise action performed by MoveNext depends on the state of the enumerator object when MoveNext is invoked:
[...]
If the state of the enumerator object is after, invoking MoveNext returns false.

The Dispose method is used to clean up the iteration by bringing the enumerator object to the after state.

• If the state of the enumerator object is before, invoking Dispose changes the state to after.
• If the state of the enumerator object is running, the result of invoking Dispose is unspecified.
• If the state of the enumerator object is suspended, invoking Dispose:
  • Changes the state to running.
  • Executes any finally blocks as if the last executed yield return statement were a yield break statement. If this causes an exception to be thrown and propagated out of the iterator body, the state of the enumerator object is set to after and the exception is propagated to the caller of the Dispose method.
  • Changes the state to after.
• If the state of the enumerator object is after, invoking Dispose has no affect.