Same thing happened to me except mine went from 3/23 to 6/22 to 6/8 to 9/5.
I punched in a couple e-mails from friend of mine that reserved a couple months after me and their DDE has NOT changed. What's up with that. There is also now a deafening silence from the dealer when I try to contact them. On 3/25 I was told that my car had shipped and I got my VIN. Now I'm not getting a response about where it might be.