This bug is slightly similar to bug 4467577.
The 1.3.1 plugin does not send the password with the URLs that
the applet opens under the following case:

- when the codebase of the applet does not match the codebase of the URL

Recreating the Problem
-----------------------
Option 1
Using the files located in the attachments
Download the three files (the JAR and the 2 HTML files) to a
server which requries authentication for every URL connection.
The server should be accessible on the default HTTP port 80.

Problem (HTTP port 80)
------------------------
- Launch the applet using plugin-test-13.html. Enter the password
  when requested by the browser and plugin.
- Access a file on the server by typing the appropriate URL. The
  plugin should not ask you for a password if it has already done
  so. Access a few more files in the same manner to make sure that
  the plugin does not ask for a password again.
- Now repeat the above step, but this time, include "80" as the HTTP
  port number in the URL. The plugin will challenge you for a password
  for every unique URL that has the "80" in it. You have to access
  different files each time.

Option 2
Access http://greatpoint.sfbay/plugin-test-13.html with Java Plugin 1.3.1.
Using "user" as the login and password. When the Applet appears enter
into the URL http://greatpoint.sfbay/plugin-test-12.html and you would be
asked to login again.
After login add the :80 port number to existing URL value
and you will be asked to login for the fourth time. The login should have been
passed on or remember.