Another data point: I have not ever seen this until just the past few days. If I log into a private browsing window, it brings up the correct page content. However, once I log into my account (in the private browsing window), either immediately or eventually after clicking through a lot of different pages, the main page will switch. Sounds like it's not a repeatable scenario by all users...
As noted by others, an interesting aspect is that the correct "member" content is always initially displayed, and then something tells it to switch to this "public" content. Hitting <esc> to stop the switching doesn't work for me, either.