Running OSB 10.4.0.2.0 (did not find dataset language reference. Created a dataset directory and placed my two default datasets in it; one dataset for default includes, one for default excludes. If the datasets are referenced by name such as "include dataset directoryname/includes", backup works just fine. If referencing by the directory name, as shown in the documentation, such as "include dataset directoryname", the backups always fail with error "no data to backup described by dataset".
Doing a dataset check for the dataset using the includes reports no errors. Only error in the referenced datasets are " include host directive missing from dataset". Do note that the example in the documentation is also missing the host directive. The error appears to be a misnomer, as the backups will complete successfully, as mentioned above. However, referencing the directory name also produces no error during dataset check, but the backup will fail, as mentioned above.