Time zone settings not respected

I have the time zone in my account info set to Europe/London, but the times on the entries are showing up as six hours behind. (Which I assume is the site default US time.) I even have a scheduled post that shows up as scheduled for 12:00PM in the edit post view:

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But then shows up as scheduled for 6:00AM when I view the actual post:

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Re-saving the time zone in my account settings didn't fix it, nor did changing to another time zone and then changing back. Everything was working fine until a week or two ago - did the Daylight Saving Time change maybe cause some kind of hiccup?