Here's a "test" site I've been using to play around with PressForward and an example post on which it happens: http://read.boffosocko.com/2017/02/09/why-republicans-are-still-struggling-with-repealing-and-replacing-obamacare-the-atlantic/ Here's what I'm noticing as

Here's a "test" site I've been using to play around with PressForward and an example post on which it happens: http://read.boffosocko.com/2017/02/09/why-republicans-are-still-struggling-with-repealing-and-replacing-obamacare-the-atlantic/

Here's what I'm noticing as I go through the process:
I used the bookmarklet to nominate the post (and in the modal window prior to clicking "nominate", the first attribution with link appears at the bottom of the page, presumably being included via Mercury--it's possible it's in the bookmarklet JS, but I'm not seeing anything that looks like that's the case with my shaky JS skills, but you may want to double check), then checking within the database, post_content shows just the single original attribution (again presumably from Mercury).
It's only after moving the post to "draft" that PressForward adds the additional "Source: URL wrapped title" attribution (with paragraph tags) to post_content which results in the duplication.