On MCPE with same home I was built (it has a portal at -1 floor underground), new Nether portal isn't creates D:
Same happens in Minecraft 1.10.2. New portal spawns nearly at my home (when my original portal is underground). When I break new portal and used my original portal, second new portal spawned nearly at position of first new portal.
On MCPE with same home I was built (it has a portal at -1 floor underground), new Nether portal isn't creates D: