I've discovered the plugin that was interfering with Jetpack. It's called "Tweet, Like, Google +1 and Share".
I think that all the people that are having problems with posting on Facebook should check if they have this ( or a similar) plugin.
Great. Another Jetpack users reported the same conflict a few hours ago. It will be fixed in the next Jetpack release. You can check the fix here:
https://github.com/Automattic/Jetpack/commit/5e9970fd6c89c92be94fd057b7155dadaf0ec4f6