I've developed the habit of checking Rigol's website for updates periodically (I own a DS1074Z) and I've noticed what seems to be a firmware update for the DS1000D/E/U.
It says Firmware_00.04.02.01.00, dated 2017-07-
17 (obviously a typo, someoned typed "1" instead of "0").
http://int.rigol.com/Support/SoftDownload/3