Static NAT statement disappears from running-configuration
Symptoms:
On a Cisco router performing NAT, static NAT statements may disappear from the
running-configuration during operation. Any new flows requiring translation via
the missing statement may fail.

Conditions:
- This problem was first experienced in IOS 12.4(9)T.

- It has only been reported for extendable, inside source static NAT statements
for TCP ports 80 (HTTP) and 25 (SMTP), with and without a route-map:

Examples:
ip nat inside source static tcp x.x.x.x 25 y.y.y.y 25 extendable
ip nat inside source static tcp x.x.x.x 25 y.y.y.y 25 extendable route-map nonat
ip nat inside source static tcp x.x.x.x 80 y.y.y.y 80 route-map nonat extendable

- After the statement disappears from the running-configuration, it is still
visible in the startup-configuration.

- Existing translations created before the disappearance are cached in the NAT
translation table and continue to work correctly.

Workaround:
Reload the router.