My world starts fine and runs OK until I build the smeltery. After that, when I'm walking forward with W, I start moving though the ground depending on where I put the mouse pointer. I "fall" slowly down through the ground/rock or back up to the surface and above if I move the mouse toward the top of the screen. When I'm first playing, I can't do that - it's just walking on a flat world like normal. I've restarted several seeds and it's happened every time. I have a quad core processor is 2.6Ghz, 8.0 RAM with an AMD Radeon 5450 video card. The specs said that some AMD cards will not work but I don't believe mine was on the list.
Is anyone else having this falling issue?
