Dave opened a conversation, read it, and then couldn't see how to get back — the wedge that opens a thread goes light once it's open, and light means "nothing to see here." His instinct was the Home button, and it was disabled. That instinct is now the design: whenever a conversation is open in the timeline, Home lights up, and clicking it closes everything and returns you to the top — the same fresh timeline Home has always meant. (Theme v0.5.317.)