I received the same email. I am keeping my order, as I have no issue waiting for additional stock. I've seen the film many, many times, and can wait to watch it again.
I placed my order with them on 4/30 (along with two other titles to get free shipping). I am still awaiting a shipping notice, too. I just think they ran out of stock, as most retailers are on back order right now. We'll just have to be patient.