Nether Portals teleport to wrong, unpredictable locations, hundreds of blocks away

[N] is for Nether coordinates.

 

This happened today and behaved in two different ways. I only have a clip of the second occurence. They are as follow:

• Entering an already built and linked portal at Overworld coordinates (82, 67, -1146) teleported me to (approximately) ([N] 82, ?y, -1146), so about the same coordinates as the Overworld source, the game failing to divide the destination values by 8 as it should have.
  • The linked Nether portal (and usual destination)'s coordinates are ([N] 8, 34, -142).
  • The game did NOT generate a portal at destination. 
  • I do not have a clip for this. I'll add one if the bug reoccurs.
• Entering a newly built portal at a far away stronghold (1065, 28, -1493) teleported me to the Nether portal ([N]8, 34, -142) that is linked to the portal from my base (82, 67, -1146).
  • Re-entering the portal led me to my base (82, 67, -1146).
  • See attachment.
  • EDIT : Keeps happening every time I try to cross the same portal. Building an output portal directly at the corresponding Nether coordinates fixed the problem.

Happening on offline solo game, survival; 187.5mb save file.

 A lot of walking ensued.