I was just editing one of my modded cells (I used the AaaMarkers cells as base) when I came across this looming in the horizon of my interior cell:
http://img812.imageshack.us/img812/7986/ckoddgrass.jpg
So what I'm wondering is - how did it end up there, and how can I remove it? Apparently this grass plane is present in every cell that is based on the Aaamarkers, so I definitely would want to get rid of all unintentional extra stuff. I don't know if the grass has some kind of effects on performance, but its mere existence is very annoying. So how does one go about deleting grass. I haven't really edited terrain before so I don't know how to erase those weeds from my cell.

It's an editor bug, sometimes when you leave a worldspace and go into an interior cell, the grass is still there. It won't be there in-game.

Ok, thanks dude. I was afraid that my cells were messed up big time. Good to know it's just some random quirk.