The default admin port has changed in each of the past three major Application Server releases. Specifically, the default admin ports in 7.x, 8.x, and 9.x are as follows:
AS 7.x: 4848
AS 8.x: 4849
AS 9.x: 4848
This is not a bug, but something to be aware of. The default admin port is just a recommendation. It is anticipated that future Application Server releases going forward will retain the default 4848 port.