When using a nested tab structure, the nav title fails to update when navigating to nested tab state

I used this codepen as a model to create a nested tab structure for my own app.

But I noticed an issue: when you navigate to “Messages” (the container of the nested tabs) in the main tab on the bottom, the nav title fails to update (actually, it updates the first time it is clicked, but then it fails to update on subsequent navigation).

Any ideas why this is happening? I’d like to avoid employing some kind of $state tracker just to get the nav title to update. I noticed that the nested tabs aren’t using an ‘abstract: true’ property – could it be related to that?