As far as I've heard and seen, having more than 4 visible portals caused the engine to freak out, resulting in visual glitches. But as of late, it appears to have been fixed. Did anyone else notice this?
EDIT: It also appears that the border for square portals now properly extends to the edges. It's great they patched this. It was an interesting command.

So I would guess it's fixed! Perhaps this opens the possibility of using world portals in coop now.