Hi Danilo,
In the current version there is a box in the blog post edit page for "Exclude from Recent Content", if you uncheck that it will not appear in the recent content feature. I'm not sure which version we added this checkbox in so you may need to upgrade.
I will log a ticket in our project tracker to investigate the recent content feature and feed because it should respect the publish begin and end dates, so this sounds like a bug.
Best,
Joe