this is extrange… if you change the Landscape scale (low values) then the paint foliage just works. In my case I just have a 1096x1096 heightmap if i select a 4000x4000 landscape scale the paint tool doesnt work at all. But if i change that scale to 500x500 the painting tool works fine. I guess this depends the processing power and video hardware that i have to process the data. In my case i have a macbook pro 13 intel iris 1.5 GB video card and 8 GB ram