Realm Spawning not same as single player / vanilla server

So i built a pigman in the nether on top of the bedrock roof assuring that i would get all the spawns (if i was alone on the realm) and i do, but for about 10 seconds then all spawning stops and i need to run around the spawning area to get new spawns. this is not the case for single player and other none-realm servers.

is this a feature to increase performance against afk players and if so add option to disable it.