FULL PRODUCT VERSION :
java version "1.7.0_147-icedtea"
OpenJDK Runtime Environment (IcedTea7 2.0) (7~b147-2.0-1)
OpenJDK 64-Bit Server VM (build 21.0-b17, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Debian Wheezy 3.0.0-2-amd64 #1 SMP Fri Oct 7 20:48:45 UTC 2011 x86_64 GNU/Linux

EXTRA RELEVANT SYSTEM CONFIGURATION :
The system is linked with a network printer (Brother HL5350DNLT) that works correctly in cups.

A DESCRIPTION OF THE PROBLEM :
When printing to a tray (so setting the Tray-option in a printrequest) the printjob sends an invalid argument-list to lpr.

I've done some testing and debuged the problem to a deep level and I noticed that in com.sun.UnixPrintJob the var mediaName is pre-assigned with a default value. If you check the code in the class, you'll see that this means that this var can never be null and that in the print-method this line will always be executed:
mOptions = " media="+ customMedia.getChoiceName(); (line 349)

If you've also selected a tray, then also the line mOptions += " media="+choice; (line 357) is executed.
This means that mOptions matches something like "media=letter media=Tray2".

I've checked the documentation (cups) and there is mentioned that
only 1 of these 2 parameters can be there (or combined with a "," to media=letter,Tray2)
For more info about these options: http://www.cups.org/documentation.php/options.html

Note 1: the same could be true for the awt-printing infrastructure (e.g. PSPrintJob)
Note 2: I've also noticed that other apps pass the tray as "InputSlot=Tray2" to cups but I didn't investigate this any further.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1) take a similar printer - a network printer with multiple trays (if possible the same)
2) create a small app that prints to tray 2
3) run the app and validate the result

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
check that the printer took a sheet from tray 2 and printed the content
ACTUAL -
printer gives an error related to the media-parameters

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
                //Assign the networkprinter
PrintService p = Printers.getPrinterByName("HL5350DNLT");

                //set tray 2 as output
                MediaTray tray2 = ... //Select tray 2 from the supported attribute list
PrintRequestAttributeSet attributes = new HashPrintRequestAttributeSet();
attributes.add(tray2);

                //Create a print job
DocPrintJob job = p.createPrintJob();
job.print(new SimpleDoc("Test", DocFlavor.STRING.TEXT_PLAIN, null), attributes);
---------- END SOURCE ----------