I always understood this as a bug that was expected to be fixed by the mapper. Basically, if a spectator is allowed to take damage/kill themselves in any kind of pain zone they will appear as a pawn and be able to take the flag thereby ruining the game. It also has other nasty side effects sometimes for spectators where their game can become pretty unstable (warping visuals while moving around). Also, there is a massive amount of spam in the server's log when this happens:
CHSpectator CTF-Lostfalls.CHSpectator6 (Function Engine.PlayerPawn.PlayerWalking.ProcessMove:00B5) GetAnimGroup: No mesh
A similar bug happened in an early version of teamswitcher, where checks weren't included for specators changing teams. Once a spectator typed !r or !b, their pawn would become visible in the game and they were then able to grab the opposing flag making it disappear from the game.
The best explanation of the mapping issue that I found some years ago was written by KillRoy in the readme of this map:
https://ut-files.com/index.php?dir=Maps/CTF/MapsF/&file=ctf-fastandfuriousstealthdp.zip
Thanks to KillRoy for sharing that information πΊ It helped me understand why some maps were screwing up years ago.
Edit: This map was removed because spectators could kill themselves in the lava and IIRC was the one where it messed up the spectator's client game after doing so (maybe caused by excessive spam in the client game can't remember for sure). Had some good games on this map years ago, too bad π
https://unrealarchive.org/unreal-tournament/maps/capture-the-flag/K/ctf-kwc-mini-boxer_bb322f4d.html