From what I understand, if a player is picked up and dropped on the same day, that player remains a free agent for everyone except for the team who intially picked him up and dropped him. I believe they have this rule to prevent the "locking up" of players (i.e. some unruly manager can pick up and drop players (and thus put these players on "waivers") to prevent other teams from picking up free agents, if the procedure wasn't in place).