Me and my sister were using nether portals (have been using this Portal for a few months now) anyways this particular time when my sister went through the nether Portal (from the overworld) she ended up somewhere that wasnt our Portal (not a problem, I thought a creeper or ghast blew up the portal again, nothing new) until she went back through the portal (from the nether) I realized she wasn't near me... In fact she travelled for 2 hours to get back home... Now I am no stranger to nether portals (have been using them for years  now) but she must have come from the nether AT LEAST 3000 blocks away. I also tested right after she went into the portal for  myself to see if I would get the same effect.... I did not and arrived in the nether at the correct portal... I am not sure what happened, but I know we were getting lag spikes when she went through the portal, could that result in anything odd? Also this Portal she arrived at had not been created by us, because we have not explored that biome before... If need be I can copy my world and turn coordinates on to see how far away she went..