The portal mechanics are pretty crazy, and here is my best understanding of the situation: (with a theory as to what happened)
Potty Mouths make their portal and go through. Minecraft generates a portal corresponding to their coordinates in the nether. (This makes sense.)
Guude goes through Nancy Drew's portal, and is close enough that he gets sent to the PM portal in the nether. (This also makes sense.)
Guude sees PM and flees back through the portal. This event spawns a new portal in the overworld. (This made no sense to me at first.)
Guude kills the newly formed portal in the overworld.
Team PM goes back through the portal as well. Half go to their original place. The other half go a newly formed portal near Guude's extinguished one. (What the Hell?)
The only explanation I can think of is the team PM's portal in the nether was spawned very far away from where it wanted to be because of bad terrain. One side of the portal was far enough away to form a new portal. The other side was close enough to go back to the original.
A similar trick is mentioned on the wiki (See "2-in-1"):
http://www.minecraftwiki.net/wiki/Nether_Portal#Implications
So basically, people who went on the "right" side of the portal would spawn a new portal, but people who went through the "left" side would go home. As soon as someone makes the new portal, it "takes over" since it is closer.
But for this to happen organically would be spectacularly unlikely. It's a stretch, but does anyone have any other ideas what happened?
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