bobrobinson I think it used too on the old platform ( i could be wrong )
If I remember correctly, it wasn’t quite like that in the year or two prior to migrating to flarum.
When you replied to a message, you had the option to change the thread title. But that was a complete waste of time, because only the opening post actually displayed the thread title. And that was the same, even if the reply had a changed title. Nobody ever saw it 😮 And I vaguely remember pointing out that it would indeed be useful if the title of the reply were displayed, but somebody thought it was more important to save a line of screen space.
Though if we go back maybe three or four years ago, before giffgaff tried to personalise lithium for its own purposes, then maybe in the very early days the thread title was displayed against replies.