Downsampling of coloured greyscale-Images
... does not work correctly.
An uncolored grayscale image and the same colored grayscale image are reduced differently
Yes, i can confirm this. Seems to be OK in InDesign (high quality) preview, but damaged in exported PDF, like in Maik’s "downsampling-bug.pdf". Tested on macOS 10.12.6 and InDesign 2018 (13.0.1).