Inconsistant streams from different sources.

I've been trying out TweetDeck for the last few days and discovered a curious thing. I've found the odd post appearing in that program that doesn't appear in my stream on my home page. How can this happen? It seems there is a flaw that may cause me to miss some updates if I where to rely solely on the twitter very web site.

I tried a refresh but the post will still be absent from the list.