Kyocera DU-31 Instructions page 14

Duplex printing from the Multi-Purpose Tray
In first mode, be sure to set the MP tray to the same paper size, paper type and feed
direction as set for the current cassette. If the paper size, type or feed direction
differs, a paper jam may result. Also note that it is not possible to select the multi-
purpose tray as the current cassette and perform duplex printing. We therefore
recommended that duplex printing be performed from the paper cassette.
Note
In the case of an FS-7000, duplex printing is not possible from the
printer's MP (multi-purpose) tray, the optional envelope feeder (EF-
1), or optional universal feeder (UF-1). If duplex printing is at-
tempted from these paper sources, the mode is automatically
canceled and the printed paper is output from the face-up tray.
When the duplex printing mode is set to off, paper can also be
output from the face-down tray. However, when feeding paper from
the envelope feeder, output is through the face-up tray.
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