Tested it in singleplayer, Nether Portals work just the way they should there.
Nether Portals seem to be severely broken in this version of Spigot.

You can enter the portals just fine, but they'd take you to random locations in the world. One time it spawns you directly above lava, the other moment it spawns you 6000 blocks high up in the sky, causing you to fall to your death. Oddly enough it doesn't make a new portal either.