I opened an ULTRA Shadow Tower portal for Weeping Prophet and cleared the first two floors solo. When I entered the portal to go to the third floor I notice that it was not the same as it was in my previous run through. As I ran forward through the dungeon I encountered another player, who was a bit shocked that I was in the HARD ST that he had opened. We had both opened and entered portals in different clubs.

Also, I just ran a Normal Hydra ST by myself, but when I went through the portal after killing the boss there was already another portal open in the room, and there was even a shadow bow laying on the ground in the room. I took a screenshot of this. I did not get to see where the strange already open portal lead through as it closed when I took the screenshot.