Tnt + Nether Portal Dupe

Singleplayer:

Light tnt next to a nether portal before jumping in: You go into the nether and the portal breaks behind you. After coming out of the portal from the nether, for some reason rather than relighting the broken portal new one spawns. You can do the same thing with the new one and another random portal will appear. (I did it 4 times in a row)

 

Multiplayer with allow-nether = false:

Hop into a nether portal, light tnt while in the portal. When it explodes and breaks the portal.