Yes the option 'CommitUnchangedObjects' is a new feature and is implemented.
In previous versions all records were always committed even if nothing was different. When you uncheck the version the module will evaluate if any of the values from the excel sheet is different from the values in the database, if there are no differences the objects will not be committed.
Not tested myself, but I think you can test this easily yourself if you check the changed date. Do a synchronize objects and simple check if the records that are not changed also have a changed changedDate. If not I would file a bug report.