[KiLLeR.]

aron9forever, already told you why this happens and I'm pretty sure there is almost no way to avoid this with random spawn generator... Best solution is to use predefined spawn positions. So, you can add an admin command which get current player origins, writes it to a file and when you want to spawn a player on random position, simply take random position from that file. You have to play a bit more with reading/writing data in files, but this gonna work better for your needs.