I experienced the same thing. I left my nuclear power plant and a small group of MV solar arrays humming away, and a rather large quarry, put on my full quantum armor and set out with a handful of Ender Eyes. I reached the stronghold, and activated the portal. I did not intend to enter, but jumped down on to the edge of it. Apparently that was enough. As you said, I appeared in the middle of nowhere. There was a huge oil geyser nearby, and nothing else. I finally threw all my stuff into a chest (forgetting my armor!), and jumped to my death. I'm now back in the normal world. ~sigh~
I'm thinking to gather up a few tools and resources and start again somewhere far away... Or should I just make a new world? Hmm.
That was a bit disappointing.