I must admit that it does appear to work - but only because the regulators happen to be half voltage of the 18V supply. Well, apart from the fact that both outputs surely must be +ve
The 7809 is regulating correctly, producing 9V - the remaining 9v are dropped across the (incorrectly configured) 7909.
If the supply voltage was for instance 24V, the outputs would be 9V and 15V.
John