Curiously, there used to be a thread on ET regarding this subject, but apparently it was removed. There were already people talking about what Lightspeed was doing at the time, a few years back.
I don't have the exact quotes, but here is a paraphrase I can give:
" Various people who have used Lightspeed trading, for example have claimed that some firm related to Lightspeed trades against its open interest (client orders). Apparently, some firm may have access to Lightspeed's Open Aggregate Position Book. Lightspeed seems to be affiliated with Schonfeld Securities. Schonfeld is an HFT firm that is housed in the same building as Lightspeed. So, basically, it is possible that Lightspeed orders get front-run by Schonfeld (similar to what happened to Pipeline Trading), and that Schonfeld trades against Lightspeed's open interest. "