Invasion of the green line

Can anyone tell me what the green "boundary" that appeared, partly surrounding my land and partly marking out a chunk of it (See picture)?

Inside the boundary the rocks remained as I remembered them, outside they appeared to have a finer grained texture. The line itself reminded me of moss and was not editable or seectable.

I've added a purple line to indicate where the boundary of my land falls, some of my neighbours land was enclosed by this as well.

It didn't seem to stop me editing or creating but what was it?

P

Something is up with the texture of land lately.. please bug report this and include the snapshot!