I'm pretty sure the map itself would have normal spawn points. If TTT spawns are not found, the default spawn locations are used.
With my experience, I've found that mappers don't do a good job and place 1 game's spawn points (such as deathmatch's combine and rebels) without the default "info_player_start", which is fine to run on garry's mod and that game but screws up when a gamemode has a defined spawn point, which it ttt's case is the counter strike source terrorist/counter terrorist spawns.
If you are spawning in walls and such, it would indicate that a "info_player_start" entity
wasn't placed since you would all be spawning on it, glitched together. Since that isn't happening, you must all be spawning at {0, 0, 0}.
Now, it could be something else, but that's my logical guess from what I've read and seen.