Oil doesn't pour?

In my last battle a Carthaginian spy opened my walled gates and the army attacked throught it. However unlike pre 1.2 no oil poured onto the advancing men. Is this correct or just a bug?

I hope its correct as now there is actually a point in sending spys into walled cities.

Hi - this is an undocumented enhancement brought in by 1.2 - I think it makes more sense this way, and anyway it gives a slight helping hand to the the AI who always drop all seige equipment and charge willy-nilly for the open gate from the get go...