Strange nether portal crash and item dupe bug (Issue with level generation)

In my survival world, I entered my first nether portal and found the fortress, and did all the normal things one does in the nether. However, a few days later, when I entered the portal with my pet wolf, I was killed by a large magma cube. I continually entered the portal over and over with nothing but my fists to destroy the magma cube, and on my third try, I noticed that the iron door leading to my nether portal room was open, which is unusual, because normally, a button must be pressed to open the door for a few ticks before it closes automatically. I didn't give it a second thought and entered the portal, which strangely crashed my Minecraft. This happened a few times before I finally killed the magma cube. I picked up the few items that were leftover on the ground and got in the portal to return to the overworld, and when I did, text popped up above my hot bar that said "loading terrain" which I have never seen before, then my game crashed for the third time. 

 

Once I had Minecraft open again, and entered my survival world, I was still in the nether, but I noticed that I had more items in my inventory than I had before, somehow, all the items I had before the game crashed had been duplicated. I returned to the overworld, and now everything seems ok, but this was weird.