Nothing is wrong. BellSouth's Multi-Static IP (5 IPs or more) service is designed to assign a dynamic IP on the WAN interface. Here's more info:

Business Multi-Static IP Service
Important Note: Please read this section carefully. BellSouth's multiple static IP service is a very complex offering as compared to traditional static IP assignment. It is different from multiple static services offered by other ISPs and requires a router (or routers) with specific capabilities and custom configurations. If you do not require multiple dedicated IPs for specific individual devices, then you should really use the single static IP service.
•Business customers can have a minimum of 5 and a maximum of 61 static IPs.
• Customer receives an assigned block of IPs from BellSouth that will include the usable static IPs as well as 3 additional IPs for:
1. Default Gateway
2. Subnet Address
3. Broadcast Address
A customer wanting 5 static IPs would actually be provided 8 IPs (5 assignable and 3 for management).
• The WAN IP is dynamic and will change (this is normal). Your static IPs are bound to the dynamic WAN IP within the core network. Do not try to assign any of the static IPs to the WAN side of the router!
• Customers are required to run a compatible router (either supplied by BellSouth or the customer) that is capable of handling the desired number of IPs. The router must also be capable of PPPoE and must be able to create a "one to one" (or equivalent) NAT for each specific device.
• The static IPs are bound to your dynamic WAN IP based on your username and the login format is username@bellsouth.net.
• If you are experiencing authentication problems logging in using the username@bellsouth.net format then there is a problem and you should contact the HelpDesk. Due to a character limitation on Cayman routers running 6.3.0 R2 or earlier firmware, you will be required to update the firmware to 6.3.0 R7 or higher.
•Configuration information is available via the Netopia 3346 BellSouth Business DSL Multi-Static User Guide.
• There is additional setup information available at the BellSouth Technical Help website, however it is completely and utterly useless. BellSouth has not corrected errors or updated the FAQ in years. Do not use the user%static format for logging in as suggested...it's dead wrong.

Andy Houtz DSL