Nether portal exit, but was not build

Hi,

i set up a single Player game in survival mode. I bulid a Nethe rportal and useed it many times.
Then today, i left the nether by using my Nethe rprotal, but not come out at my home in the uppe rworld. I come inside a mountain in a verlies of Spiders.
It is arround 150 or 200 blocks away from my home and bed Point.
I have not been in thsi verlies before. So I think thgis is a bug!

Kind regards
Rainer

P.S. Sorry for my terrible english. but it is better as my dansk. By the way, taler du tysk?