Andrew, I'm noticing something very similar with one of our sites www.intervention-referral.com
I have an extra 320 linking root domains this month all coming from High Domain Authority sites within deep subfolders and subdomains. According to OSE they all use the same "intervention" anchor text and link to our homepage. However, all the URLs in question point to files that prompt downloads like pdfs, .ppt, .img. etc. I downloaded a few and could not find our text link anywhere. Here is a sample:
BTW - We are not outsourcing any seo services so I'm very confused as to what's going on.
Thanks,
Aaron Brownell