Kouichi Matsuda at Sony provided a test case (attached) which renders incorrectly on a Windows 7 machine with an AMD Radeon HD 6970 and driver dated 11/9/2011. The correct rendering is a red point in the center of the black canvas; the incorrect rendering is just a black canvas.
(I have not been able to reproduce this locally due to lack of hardware.)
In the attached archive, HelloPoint1.html renders incorrectly on AMD hardware but correctly on NVIDIA hardware. HelloPoint2.html renders correctly on both vendors' hardware. They differ in how the positional data is passed into the vertex shader.
A test based on this issue should be added to the WebGL conformance suite version 1.0.2.