RSS feed: Posts Limitation

First thanks for this great piece of technology and to the community!

I am experiencing a problem with my RSS feed 2.0.
I noticed that since the last two posts I released that my feed is like limited in the number of posts is showing.
The very first post have been removed and I posted a new post yesterday and now it’s post n?°2 that dissapear from the RSS. It’s like everytime there’s a new post the older one is removed.
I searched options and changed the RSS syndication limitation of posts to 50 but it seems that doesn’t change anything.
I would be greatful if someone have the answer!
Thanks a lot!