It seems all posts are have double the amount of space between paragraphs now. If you're in the post editor you would normally hit 'enter' twice: once to go to the next line, again to create a paragraph break. Now, that will create double the amount of space.
HTML-wise, that creates 4 <br> tags. Interestingly, the post content isn't inside a paragraph tag, it's just directly after the parent <div>. There is then an empty
paragraph tag after the content. The forum could be inserting the post content before the paragraph instead of inside of it.
e.g. it's doing this:
instead of this: