There is a bedrock glitch, which is happening with portals that are too far from spawn (I don't have the exact distance) where once you go back in the Nether it'll teleport you to the edge of the world with an error message, and players will die in the bedrock/void.
I want to avoid using vanilla worldborder, since it doesn't show in the dynmap and I hate squares.
This gets fixed with PaperSpigot though, but I'd rather use Spigot.