I have found out why my entry titles are removed in all planets.
Wordpress recently added in their feeds a new tag in each item of the
That's the one which get caught in feedparser, instead of the item real title. This bug was already noticed and added in the bug tracker: http://code.google.com/p/feedparser/issues/detail?id=83&q=wordpress.
So I guess it's just a matter of time for Lennart, me, and some other people, to appear right in all Planets.