It's not a bug - it's the result of trying to balance ease of use with speed. When Auto is applied to multiple images (as in Import, Grid, AutoSync), LR doesn't calculate each image's Auto settings - it uses the most-selected and applies that to the rest. So let's say you applied Auto to a batcch of images. When you then take any individual image into Develop you see that the Auto button is enabled, indicating that that image's settings are not Auto.