Going to the nether and back won't update worldborder size for the client.

The worldborder is 8x smaller in the nether than it is in the overworld so it is very likely to spawn outside of the worldborder when going to the nether. There is no way back because you can't move out of the portal to re-enter it.
If you set your gamemode to 1 then you're able to go through the portal again. Although when arrived in the overworld it still applies the bordersize of the nether to the player which means he can't move. Relogging nor restarting Minecraft fixes it. You don't take any suffocation damage though.