Illustration of an unexpected behavior of the K-Stacker algorithm when using a noise-weighted averaged combination of images. Top panel: best orbit found by the classical combination algorithm, and bottom panel: best orbit found when using the noise-weighted averaged combination for the same simulation. In this case, the planet has a S∕N ≃ 1.9 in the first four images, and ≃ 1.2 in the last six. The real orbit of the planet is in black.