I'm not really sure what I deed wrong. My guess is that it's because I updated some of my old posts for linkbuilding purposes and published it.
The thing is, I did not change the date and I have done this in the past without this unwelcomed effect. If you had encountered the same problem and know of a fix to this Feedburner Sending Old Feeds problem, please share.
I have just Ping my Feedburner feeds and resync it as well. I hope this will fix this error.