Starting or Restarting a Copy Group
When a copy group is started (or restarted), the remaining input data is forced to the start on the next sheet. Therefore, if duplex output was expected, but the copy group is restarted while processing the front side of a sheet, the remaining data starts on the front side of the next sheet rather than on the back side of the current sheet.
See Duplex Output with Different Front and Back Print Directions for an example.
Furthermore, observe that any copy group action except NULL restarts the page format (see the following item).