"Files" sidebar is not expanding folders when navigating to subfolders

Created by: mrnugget

• Sourcegraph version: Sourcegraph.com
• Platform information: Chrome

Steps to reproduce:

1. Go to https://sourcegraph.com/github.com/sourcegraph/sourcegraph
2. Click on the cmd folder in the main view (not the file sidebar!).
3. It looks like this:

4. Click on a subfolder, like `frontend`.

Expected behavior:

I expect frontend to be shown in the sidebar and to be also expanded.

Actual behavior:

cmd is still highlighted, but not expanded and frontend is not shown.