I have noticed that whenever I edit an old post I get tweets sent saying such. Although not really annoying it does mean that minor adjustments get tweeted.
So I have adjusted my automatic Twitter settings so that when I edit old posts they will not be tweeted. Just did an edit of tags (or at least added some) and now have lots of tweets about these. Should have studied the WordTwit settings a little more closely when I installed it. Issue should now be sorted.
Mind you, virtually no-one follows me and pretty much no-one reads this website!