Lava kept blocking the pathways, so I decided to try and block it up. That's when I discovered they did something to at least lava physics in The Nether. It can keep flowing from the tiniest amounts. Lavafalls can continue from absolutely nothing at the top, where as I used to block the floor off the edge and it'd slowly stop. Maybe it's always been like this, never thought to stop lava there before, but still...