This problem has only occurred since the recent Minecraft update. Sometimes but not always when I enter a portal I am delivered to a random location. The first time it happened I entered from the nether and ended up in a random overworld location. at the time I did not note the coordinates on both sides so I do not know if there was a correlation. Since then it has happened twice more with an overworld portal where it delivered me not to the connecting nether portal but instead to the same coordinates in the nether. Since my overworld portal was at a very high coordinate number that meant I had a very very long trip home. It does not do it every time and it is very frustrating to have to travel 20,000 blocks home for no reason. I would like to stress that no portal was generated at the destination either time.