The roster at milb.com is not complete. For example, Jamari Baylor led off today for the FCL Phillies - but he's not listed on the roster! This is true of a couple of other guys in the lineup today (Gonzalez, Pineda, Viloria). I presume the data entry people at milb.com will get caught up, at some point...
The extraordinary thing, to me, is that the web sites' various pages do not seem to pull from a unified back end. So there are transactions listed on individual player pages that do not appear in the league transactions, and that do not result in players appearing on the rosters they're listed as assigned to. Jamari Baylor doesn't appear to even have a player page - he doesn't come up in searches at all.