Seems I just made a post 1 hour into the future and with that, on a different day. The WordPress settings say

Unfortunately, you have to manually update this for Daylight Savings Time. Lame, we know, but will be fixed in the future.

Lame indeed, and guess I forgot about this. A while ago a colleague encountered a similar problem in phpBB. Guess it’s PHP related and not just WordPress, as both products have the same problem. I wonder if the fix promised by WordPress is waiting for daylight savings time to be abandoned as idea, since it’s advantages are still being questioned.