Draw inside not working inside Expanded shape

I really enjoy this new draw inside feature in Illustrator. But, I find that it does not always work. It seems to be grayed out sometimes. For example, I have drawn a shape with my Wacom tablet using a blush.  I then converted it to a shape instead of keeping it a stroke by expanding it. But it will not allow me to now draw inside of it, even though it is a shape. Please advise me as to if i am doing something wrong.

Thanks.