Nether portal always takes player back to Nether

After going through the nether portal from the overworld, player is transported to the nether.
After leaving the portal and going back in, the 'Downloading world' screen is shown and once it has loaded, the player is transport back into the nether.
This happens with multiple portals and always transports player back to nether, i.e. stuck in Nether with no way out.