After reading Migration of content from ROS and Gazebo Answers Scheduled!, I see that the content of answers.gazebosim.org was also migrated.
Therefore, I can only assume that the migrated question that I am looking for was deleted (for whatever reason) and is no longer visible - which is a bit of a shame.
So, it is quite lucky that the old site is still up, and that the old question (and answer) is still visible.
I know that answers shouldn't have follow up questions in them, but that does beg the question: How long will the old site be up for, and how long will all the old questions still be visible?