Players at > Y=128 are set above the spawn point upon reloading the world if above a platform at height limit
Players standing on or above platforms of solid blocks at Y=127 will be placed several hundred meters above the world spawn point, and sent a client message "Your home bed was missing or obstructed".
In the Nether, the player will be placed at a location, still in the Nether, that correlates (based on 5 Nethers) with the overworld spawn point.
Confirmed in Creative and Survival mode. LAN client behavior not tested.
Created Issue:
Players at > Y=128 are set above the spawn point upon reloading the world if above a platform at height limit
Players standing on or above platforms of solid blocks at Y=127 will be placed several hundred meters above the world spawn point, and sent a client message "Your home bed was missing or obstructed".
In the Nether, the player will be placed at a location, still in the Nether, that correlates (based on 5 Nethers) with the overworld spawn point.Confirmed in Creative and Survival mode. LAN client behavior not tested.
relates to
Testing is prevented by MCPE-10951.

Please search reported issues BEFORE posting. Resolved - Duplicate
MCPE-10858. That's a joke by the way. Mod humor.Haha. Anyway, you're right: they are likely related.
Fixed as of 0.13.0. Players now remain in their previous position, or are repositioned to be standing atop the platform if above it previously.