The Java Plug-in 5.0 documentation has this to say about that strange behavior: “If Mozilla and Netscape 7 are both installed and <APPLET> tag support for Mozilla and Netscape is disabled (unchecked), ...

When used with ODS, procedures GCHART, GCONTOUR, GMAP, GPLOT, and G3D enable you to specify DEVICE=JAVA on a GOPTIONS statement to generate graphs that are Java applets. These same procedures enable ...