I just got a Wytron DVD-399 with Pioneer 10D drives.
I've updated the firmware on the 399.
The drives will not burn when the copy selection is picked. If I emulate/copy then it will work (most of the time, sometime it will only burn one of the disks).
When I select a Copy function, it gets to the screen where you'd see the numbers for burning, and the timer starts, but the data counter and buffer never do anything. They stay at zero.