I set up a scene with a glass sitting on a plane with wood texture and I wanted to see how it looks. I rendered it and the glass and it's shadow was pretty noisy. I tried increasing the samples from 128 to 1280 but it became even more noisy and the shadow became weird. I tweaked around the settings and I found out that if I disable Multiple Importance for the light source, the noise goes away. But why is this? I heard that MIS is supposed to REDUCE noise, not increase.. Images: Since I can't post more than 2 images I zipped them (also, I included the .blend too). [LINK]
filenames: glass [samples] MIS [ON/OFF]
I used cycles renderer.