Cycles does sRGB->linear texture conversion after texture interpolation instead of before. This leads to incorrect results.
Example scene is attached. Two squares with a fine checkerboard texture, one with linear interpolation, the other with closest interpolation.
Expected result: Both textures should render to an identical shade of gray. When switching the texture color space to "linear" instead of "sRGB", the result should not change as the texture contains only pure black and white pixels.
Actual result: The textures show different shades of gray. Switching the color space changes the result.