How did you manage to get to those places?
Though I am not him, I remember seeing a video. There's a way to get to GM Island though it is highly buggy and doesn't always work. I remember some dude did it from the one caves that you exploit to take you to the Outlands. He went into the ocean, swam a bit, then went up and he was on GM Island. However, if a GM finds you there you are fucked.
Reason it doesnt always work is because GM Island is there, but around it is the "Void". Its why you cant even fly into GM Island. Its this black space that is basically unmapped area. If you fly into it, you fall to your death. If (on a Private Server), you walk on water into it, you fall to your death.
If you use the water glitch to get in, sometimes it takes you (uhhh how to put this). through the Void. Without going through it.
Like
-------||||----- = Normal. (| = Void)
Through the water glitch:
------->>>>------- = Water Glitch. You'll be swimming then the game will load and take you completely through the >'s.