I'm having the exact same issue as this report: MC-89928

When going to the nether, I spawned near the bedrock ceiling in a cave, without a portal near me. The division by 8 rule didn't occur for the nether, so I teleported to house's coordinates in the overworld, in the nether, 7000+ blocks away from my nether-side portals. After relogging, a portal spawned next to me, but when I went through, it made me appear in the overworld 49,000 blocks away from those coordinates, I'm playing on the latest version, in a realm.