Back gesture doesn't work across sidebar subpages

The user can't swipe back across a sidebar subpage. Here's a video demonstrating this:

Steps to reproduce:

Open GNOME Settings (Version: aa0adcaa)
Make the window small so the leaflet folds
Pick a page with a subpage in the sidebar (i.e. privacy, applications)
Pick an element from the subpage
Swipe back. It behaves correctly
Swipe back again
Observe bug: it doesn't return back to the top-level sidebar page