The release build downloads jcifs.jar, as it should, and then proceeds to build the jcifs connector. Then, it creates the dist/connector-lib-proprietary directory as it should, having the jcifs.jar in it rather than the jcifs-README.txt. When the release binary image is made, it excludes all jars from dist/connector-lib-proprietary, also as it is supposed to - but then there is no jcifs-README.txt left for the user to notice.
There are two options here. First option is create a stub for jcifs.jar, and then take steps to not download jcifs jar during the image build. Second option is to create jcifs-README.txt regardless of whether jcifs.jar is present. Unfortunately, the build logic currently may use the existence of the jcifs-README file to decided whether to enable the connector in the connectors-proprietary.xml file, so this may be tricky.