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 feed:
tarek

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.