I have registered and logged in. Going to the Forum and the clicking the Powershell Q&A forum, the display for that forum shows Log In at the top left.
Other Forums show me still logged in.
I’m sure I’ve done nothing wrong. Is this a WP problem?
It’s a caching thing. Hitting Refresh in your browser should take care of it.
Shift+Refresh if needed. It’s your browser caching the not-logged-in page.