Thanks Awan, but may be I failed to explain the problem. No modification was made to widgets/fp-latest-posts.php except a change in the number of posts to be displayed.
‘posts_per_page’ => 3
was changed to:
‘posts_per_page’ => 6
That’s all. Naturally, restoring the original file does nothing, except that the 3 latest posts are shown.
I will leave the widget with 3 posts for now, hoping that wou will find a way to solve this in the meantime.
Note that the same posts are displayed correctly under category or tag pages. The problem is only with the latest posts widget.