No paragraphs

WordPress has started stripping all my paragraphs and line breaks from my posts, apparently. Everything is vertically spaced nicely in the editor itself (both visual and HTML), but the post then has no paragraphs whatsoever.

I don’t believe it’s a CSS problem (which most similar-sounding posts seem to be about) because the HTML source for the resulting page does not contain any p or br elements, it’s just the text with carriage returns inside the entry div. (If anyone would like to check for themselves: https://oj.hwel.de/o-paragraph-where-art-thou/)

I host another instance of WP on the same site which does not have this problem. I have also tried turning off all plugins with no change. Also, I’ve just upgraded to WP 2.6.5 today (deleting wp-admin and wp-includes) with no effect either.

The only way it works is if I manually enter p tags in the HTML editor and then never switch back to the visual editor.

(I had misunderstood this problem and reported it yesterday as Using HTML editor messes up p tags.)