I've seen Comcast do this before on a business account that was paying for Static IP.
When I called about the customer's account, Comcast said they get up to 10 static addresses for the service. And for whatever reason, they handed out 9 public IP addresses for the 9 devices the customer had at the time.
I educated the customer a little on DDNS services. We dropped the static IP service, saving him a ton of money. And I set up a new network for him that got everything working the way he needed with all the new devices and equipment.
Comcast has some really dumb people working at their tech departments too.