I have seen the same with my new site, i guess it is something with feeds (not sure), they get the first pharagraph with a script and automatically post on a website. They leave the Original Post from: phrase there and a link to your own post (maybe they think this way they cannot be accused with stealing?).
I think it can be damaging because of duplicate content (even it is only the lead of the text), but someone with bigger knowledge could clear this up for us? The threat could be that they are scraping the text almost at once when you post your article, so maybe it is hard for Google to decide which is the original text. (that’s why i think it is related to feeds as they are updated at once too in an xml format, which can be easily scraped then).
Maybe a Google reporting can be helpful?