The message format string for appletviewer.main.warn.prop.overwrite
in share/classes/sun/applet/resources/MsgAppletViewer.java is broken.

The single quote character in "user's" needs to be "user''s"
(double quote characters) as in all the other format strings in the
file. The incorrect quote character prevents the string substitution
fields in the format string (as in {0}, {1} and {2}) from being
substituted. The resulting message seen by the end-user currently
looks like this:

Warning: Temporarily overwriting system property at users request: key: {0} old value: {1} new value: {2}

While you are fixing the bug may I suggest simply deleting it entirely?
As a user I don't even want this message.
It is generated as a result of my passing in system properties on
the command line as in "appletviewer -J-Dmy.property=some.value ...".
I just went to the trouble to type that long command line and the last thing
I want to see is some huge 100+ character warning message wrapped around
my terminal window.

This message is new to 1.3. It did not exist in 1.2.2, 1.1.x or any
previous Java release. Please just get rid of it entirely.