There is a rule that says a player taken from another team's practice roster must play in the next game. This is meant to prevent teams from snatching players like Harrell from practice rosters before they're ready to play. The problem is that it doesn't say HOW MUCH they must play. Taking one snap would qualify. And nothing says that they have to play in the next game, or the game after that, or the game after that,...
The rule itself is a good one, but perhaps needs some tweaking. It was instituted because teams with a lot of depth at one position would sit a guy on their practice roster, even though he could be a starter with another team. Often these guys would sit on the practice roster for years, completely unused, because no other team was able to offer them a spot on their active roster.
I think the reason the league began to allow an active roster larger than the game-day roster was to stow players like Harrell away where no one could get to him. I guess teams are doing this, but using the IR as a way of hiding more players.
Under any circumstances, though, I don't think a team should be allowed to remove a player from the 9-game injury list until nine games after they were put on. If they can, what's the point of having it?