Same problem here:
"Winter Portfolio http://shar.es/Y4upD via @sharethis"
That should link to http://www.attitudedesign.co.uk/2013/winter-portfolio/ but it's linking to http://www.freebooksource.com/?p=59152
Obviously this is a big problem as you think you're sharing a link with your followers (in some case thousands) and it turns out it is going to the wrong website, not even related to the website it came from.
I have a feeling this might(?) be to do with the URL that the plugin provides, for example:
I think this should be the full URL.. that might fix the issue.
Again, as the OP says this is also happening on our LIVE site: http://www.attitudedesign.co.uk/2013/winter-portfolio/
I look forward to responses.