Since I'm stuck in a server teleporter thingy on SMP8 right now, I decided to make this thread until I figure out how to fix it. I suggest that the server should automatically move you to the spawn of the server you were just on, so this doesn't happen when you try to come back.
Which specific spawn are you speaking about? All should be spawning correctly. Player connection lag can place them in the floor though and that's not something that a change of smp will fix.
I fixed it by using Minechat, which teleported me to the spawn upon connection. When I tried to join SMP8, I landed on the teleporter, which brought me to SMP3 (that's the one I went to).
I have seen this a few times myself. Was wandering at first if it was ddos but that was months ago. Now it seems like background noise I have seen it so much. Never new what was causing this though. Interesting
When a server is down and you try to connect to it, it does this. There may be other ways but this is the only cause I have personally seen (other than intentionally doing it)