The metric margin values should be fixed now, however, the next time you get a new version of jEdit, you'll probably still be seeing the decimal point the first time, so you'll need to change those. Another option is to delete the 'printspec' file in your jEdit settings directory before restarting jEdit, however, that will also delete all your other saved printer settings.
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?