Incorrect Spawn Point "Y" if you exit from the map and then enter again , it happens many times (It happens in 0.4.0, 0.6.0 and 0.6.1)

In 0.5.0 the spawn point Y was working perfectly but now im experimenting this BUG.

What happened:I was digging straight down and then i made an underground cave, so i exit out of the map to the main menu, then i return to the same map and i spawned at the top, X and Z is working perfectly but Y isn´t working.

Thanks for reading my problem