For a reply with my thoughts, I wouldn't at all be surprised if this is in how MTGO evaluates P/T with Tarmogoyf (*/1+*) versus Souls of the Lost (*/*+1).
Kinnan, Bonder Prodigy and Gwenna, Eyes of Gaea do not interact as they should on MTGO. Gwenna should add 3 mana when tapped while Kinnan is in play, and it currently only adds 2. Would it be possible for members of the MTGO crew to look into this? Thanks!