So I got this WordPress plugin Twittertools from Alex King which promises to publish your blog posts to twitter including an link back to your blog post. Unfortunately there is a hardcoded tweet format setting in the twitter-tools.php file:
$this->tweet_format = $this->tweet_prefix.': %s %s';
which doesn’t provide enough %s placeholders for the URL to be posted. So if you have experienced this problem, just change the above line to:
$this->tweet_format = $this->tweet_prefix.': %s %s %s';
and all is fine.
UPDATE: This issue is fixed in Version 2.2.1, no need to patch your TwitterTools 😀