Groovy MockFor demands not acting as expected for stream

I wanted to create a unit test verifying that a stream was closed. My class decorates the stream it receives with DataputStream, which seems to break the mocking demands feature.

void testBadMock() {
    def mockInputClass = new MockFor(InputStream)
    mockInputClass.demand.with {
        close() {}
    }

    def mockInput1 = mockInputClass.proxyInstance()
    mockInput1.close()
    mockInputClass.verify mockInput1 // passes

    def mockInput2 = mockInputClass.proxyInstance()
    new DataInputStream(mockInput2).close()
    mockInputClass.verify mockInput2 // fails
}

I checked the source code for DataInputStream, and as expected, the stream passed into the constructor is the object which it delegates the close() method call to.

def fakeInput = [close: {println 'I was called'}] as InputStream
new DataInputStream(fakeInput).close() // prints 'I was called'

I see no reason why my mock object is not seeing the close() method call.