From looking at our current code, and your description, it sounds as though the game mode your using modifies Gmod's spectate and or spectateindex commands (or hooks)
Which, for a gamemode, are perfectly "ethical' things to do if they have a "spectator" team.
I'd still recommend you ensuring you have the latest ULib and ULX from github. I see we changed code in Oct 2014 re: spectate and TTT.
Perhaps it might help with prop hunt and your issue (though, I doubt it, as again, it sounds like prop hunt has modified spectate functions or hooks related to it.)
As this isn't truly a 'help with use or issue/bug" of ULib or ulx, I'm moving this thread to developers corner.