It seems that it needs to sample more tweets. I've done 5 tweets, and 2 of them were exact tweets that I sent (they were only a few words long, and I guess they had words that I rarely tweet, so it had few or no other ways to go once it started repeating the tweet)
Edit: Then again since there are only a few words in a tweet, you'd have to go a really long way back to really ensure that won't happen. Possibly farther back than Twitter will let you.
Oslaka died 2 kilometers in order to come from seafaring folk, so I do it. I spend twenty minutes left! He is hideously scarred. My host removes his face a lot in college.
Edit: Then again since there are only a few words in a tweet, you'd have to go a really long way back to really ensure that won't happen. Possibly farther back than Twitter will let you.