Nether Portals created in destination world when using teleport portals

[Melonify]

On PaperSpigot, when teleporting using a portal sign with a nether portal or end portal, the player is put about 5 blocks below the destination and a nether portal is created at the destination. This does not happen when using a water portal.

[Melonify]

Unsure if this issue happens on Spigot, or just on Paper