Yeah, I agree that it's annoying if you are being asked for selling something that was already sold... But then again, it's up to you as a player to deal with this. Prisons are cheap, so it's not terribly hard to have two at least. But if it's about UI, then the player can hardly do something about it.
Still, I agree with you Meridian that being asked about someone you no longer have is pretty bad. Actually I think it deserves to be called a bug, and not really acceptable. So... well, it would be great if you could do something about it.
Prisons are cheap, but building space is very limited.
I really have no more space in my main base to afford another prison.
Two hangars, 3 barracks, one scientific building each + 5 extra study rooms, radar, prison and two big stores.
Unless I resort to slavery -- and I swear by Cthulhu I never will -- I have no more options.
Well, from my point of view, removing the prisoners from the sell window isn't a good idea - sometimes I sell them from this window, sometimes I'd rather wait for the 'prison is full' message, sometimes I enter the prison and sell them manually. This 'upgrade' removes one of these three options, which is bad. The best would be disabling the 'prison is full' window if you sell enough hostages (stuff is moved to temp 'storage' -> loot sell window -> only then check base capacities). But if it's not possible, I'd rather have stingy players who constantly run at near-100% prison capacity annoyed, than the rest of us bereft of an useful option. Moreover, it makes tracking prison overcrowding much harder to keep, as instead of naturally selling off needless captives immediately, you have to enter the prison manually and check all the stuff by yourself (I'm talking as a player who always aims to have at least 6-7 free space in prison). So players who try to keep prisons half-empty are effectively penalized for their foresight and planning.
Besides, removing prisoners from the initial sell list is very misleading IMO - the player might get confused whom, if any, did he catch.
Yes, I will fix it somehow.
Btw. you can still see who has been captured in the Loot window.