There are two problems here:

1. the undeathinators at the spawn stations (2 2 2) are not working
   1. get there press R on them and you wont see a green box for spawn point set
   2. on suicide you will not spawn at that undeathinator

2. the spawn at a placed undeathinator isnt working properly
   1. place a station and a undeathinator on it (best only the first station block with the undeathinator)
   2. save your spawnpoint here (you will see the confirmation message)
   3. suicide and observe your respawn point
   4. place a core as marker and suicide again
   5. you will respawn away from the core on a line with the undeathinator ... this continues without end
      
      this is mostlikely a side effect of the fix for the item drop on death bug T196