End gateway spawned connecting to a location I previously was

I have no idea what caused this or how it happened, but I will explain the sequence of events that occured before I found and used this gateway.

First, I went to a location around 30000000 ~ 30000000 through teleport. From then I wandered the area, taking a few screenshots. After this I recall returning to the overworld. Then I updated from 15w31b to c and rejoined the world, from which I went back into the End. This time I found a new dragon spawned and so I killed it by setting its HealF to 0. Then I sought out the new gateway that formed and I entered it. About 200 blocks from there I happened across a mysterious gateway that had also spawned there. I teleported in and it took me to, of all places, 29999697 65 29999559. Pretty much right back to where I was at the start of all this.

Here is a screenshot depicting the blockdata and location of this mysterious end gateway that somehow connected to my past location: http://i.imgur.com/iFgo1HW.png

Block data:
{x:899,Life:21992L,y:85,ExitPortal:{X:29999702,Y:177,Z:29999558},z:902,id:"EndGateway"}

Seeing that the Life tag is 21992, this seems to be about 18 minutes that it has existed. Including the time I was not on the world plus this 18 minutes, this may have coincided with my time at the world edge. Perhaps the gateway was created while I was at the edge, but as to what triggered it, I haven't the slightest clue.

UPDATE: I visited the exact exit portal location to find another portal there. It is not surrounded by bedrock. I also did not set this here. Currently, I have no idea which portal created which portal. Here is a picture of the second portal: http://i.imgur.com/EASTOD5.png

Second portal block data:
{x:29999702,Life:7665L,y:177,ExitPortal:{X:900,Y:85,Z:902},z:29999558,id:"EndGateway"}

If anyone has any ideas as to how this happened and whether this is a bug, or perhaps something to do with how minecraft is creating end gateways somehow (I didn't know it made new gateways other than the ones from the main island to the outside islands), please do tell.

Edit: World Download: http://www.filedropper.com/snapshot19 loading world spawns at the second gateway near the world border.