Spawnpoint doesn't work with relative co-ordinates

A command block system triggered by an execute on @a within a cubic radius and using a scoreboard operator i.e.

"execute @a[x=116,y=55,z=-68,dx=57,dy=36,dz=191,score_Potion_min=1]"

triggers a second command block to perform the following

"spawnpoint @a ~1000 ~1 ~"

which returns

"[12:17:09] Set NicholasHills's spawn point to (1150, 60, 15)"

However upon player death the player is told their home bed is missing or obstructed and they are returned to worldspawn. This is tested in an open flat are where the spawnpoint is not being set inside a block.

It is likely that the chunks in which the spawn is being set (exactly 1000 blocks away) are not loaded at the time of the /spawnpoint command being executed. Could this in some way be impacting things?

Note: The ~1 on the y axis is to avoid issues noted in https://bugs.mojang.com/browse/MC-141 thus why this issue is not believed to duplicate MC-141.