The activity log was useful in pointing out that I had bad values set for the default metric margins.
As for the duplex issue, I've checked the code carefully and can see that the proper printing attributes are being sent from jEdit to the printing system. I also discovered that my color printer will print duplex, but I also can only seem to make that happen by going to the operating system printer set up and setting duplex there. The process is jEdit sets up the printing parameters, sends those to the JVM printing system, which passes them on to the operating system printing system, which loads the proper driver, which translates the printing parameters so the printer can understand, then sends it to the printer. Somewhere along the way, the duplex setting is being ignored.
I can't help but think this is a bug in either the java printing system or the printer driver.
In the "Print..." dialog, under the "Appearance" tab, there are radio buttons for "One side", "Tumble", or "Duplex" printing.
When I select duplex printing, the printer properly "prints" both sides of the paper, but the back side is blank. In other words, the front side prints, the printer retracts the page, and the back side prints; but all the text is on the front side only.
Other applications (e.g. acroread) print duplex properly using the lpr flag "-o Duplex=DuplexNoTumble").
How can I find (and fix?) the command jedit uses to print?