For an applet, I would have thought that the only version of Java that mattered was the one on the client browser's machine, not the server. The PrintApplet.jar file was last compiled on Feb 7, 2003 (as far as I know, it was probably compiled on a Windows box). The has been used to print 200,000+ labels in the past year or so (on a few thousand client machines).
Currently, when the server is either the current production Windows one, our dev Windows one, or our dev Linux one, the client browser that loads the applet and prints to a thermal printer has no trouble. But when the webserver is the new Linux one that's outside of our internal network (that we access by public IP), only the left 3 inches of the label is printed, and it's centered on the 4-inch wide label (whereas the typical/correct behavior is for the printer to left-justify it and the image ends up filling the entire width of the label). This happens even though we're sitting at the same client machine/browser/printer when we test all the 4 different servers that send the applet down to our browser. Very strange.
I'm going to try to see if I can figure out how to recompile the applet source on the Linux server in the way it's supposed to be packaged, but if that's the difference, then I guess write-once-run-anywhere won't apply in this case.