ZIP file task uses file paths as-is, i.e. with Windows style backslashes, whereas PKWARE's ZIP file specification explicitely requests that only forward slashes are to be used.
Linux' "unzip" actually creates all files as desired, but prints a warning when detecting backslashes and terminates with exit code 1, which causes a FATAL ERROR in subsequent build tools.
Please replace all backslashes in file names when adding to the ZIP file OR make this a configurable option.
The location to do this is probably ZipFileVisitor.java line 123. I'd like to provide a patch myself but am currently not experienced enough to apply changes to the Java code.