Civil Engineering prevents building of walls (Not a Bug)

[opscomm]

In this playthrough as Greece, as soon as I finished the civil engineering civic, I was unable to build or purchase any walls for my cities I had researched at the time, ancient or medieval walls.

In order to reproduce this, simply load the save, let civil service finish, and you should not be able to build walls in any cities.

This bug is for version 1.0.0.26 (221715)
The Aztec DLC is enabled, not sure if that makes a difference.

 

[Browd]

You are researching Civil Engineering, which unlocks "Urban Defenses" -- giving every city 200 fortification HP and the ability to bombard. That obsoletes ancient, medieval and renaissance walls.

Unfortunately, if you already had walls in a city, getting Civil Engineering/Urban Defenses does not eliminate the maintenance cost of your existing walls, and there's no way to remove existing walls.

I've changed the thread title to state "Not a Bug."