If a team has released a player and didn't un-check the trade box, it makes no difference as they will show in the FA lists as well. If you're unsure, copy and paste the player that you want from the trade block list and paste the name into the manual player search.
It is what is ... It just doesn't make sense to have players on the trade block that are untradeable because they are actually free agents. You then have to move over to the free agent list to get them.
Whoops, I did that in the beta version but forgot to back-port it into 0.2.2. I'll go through and purge the trading block of players who are not on a team.