As I understand it, information leaks in certain specific situations, such as when switching servers or connecting to a different network. But if the connection is stable and for a normal, everyday threat model, it doesn’t seem like a huge problem. I mean, all the pages you’ve visited in the last 20 minutes aren’t going to leak if, say, you switch servers or momentarily reconnect to the network. I think PG’s recommendation is still a good one.
If anyone can contradict me and argue that more information does leak, go ahead. I personally follow PG’s recommendation precisely because all I’m looking for is to protect my browsing habits from my ISP.