Not sure if this is a bug or not but it is definitely odd.
http://imageshack.us/a/img171/4281/20121006123210.png
http://imageshack.us/a/img94/2679/20121006123524.png

EBXL build 3.0.8.81
Forge build 4.1.4.298

This is bleed from the nearby jungle, but it should not bleed over that far.

That happens in all my worlds. For as long as I've played and there have been vines. They attach and spread onto almost any block be it terrain or building so once they are started they just keep going. I think that as long as you have extreme biomes next to each other it will happen...such as jungle/snow or jungle/desert. I'm guessing it's a vanilla issue since it happens whether I have any mods installed or not.

Thanks @Annysia

OK...that answers that!