This regression is introduced in b23 PIT.
The correspondig CR 6695124 filed by Sergei is closed as duplicate of
6705524 - OOPP/General: Concurency issues (properties r/w, JREInfo r/w, CleanupThread, removeDuplicateEntries)
6705524 is in Fix Available State and integrated in b26 PIT.

The testcase provided with b26 PIT
http://j2se.east.sun.com/deployment/www/tests/1.6.0_10/6705524/
is not failing.So filing another bug to track this issue.

Double entries in Java Cache Viewer/Applications after
javaws -import http://nicole1.sfbay.sun.com:8080/JavawsMustangIntegTest/extensionInstaller/install_demo.jnlp /
javaws http://nicole1.sfbay.sun.com:8080/JavawsMustangIntegTest/extensionInstaller/install_demo.jnlp /
javaws http://ebugster.sfbay.sun.com/dev/ebugster.jnlp
  

All platforms:
To reproduce:
- install build 26 PIT (any build from 6u10b23)
- clean the cache
- javaws -import http://nicole1.sfbay.sun.com:8080/JavawsMustangIntegTest/extensionInstaller/install_demo.jnlp
- open Java Cache Viewer/Applications
- you will see same application repeated twice: Java Web Start Extension Installer -- Installing Demo Extension
- open Java Cache Viewer/Resources
- you will see there: 6 entries: testdemo.jar, installer.jar, testdemo.jnlp, install_demo.jnlp, demo_ext.jnlp, Button.jpg

Same scenario for build 22 you can see only one entry in Java Cache Viewer/Applications : Java Web Start Extension Installer -- Installing Demo Extension
and only 5 entries in Java Cache Viewer/Resources - install_demo.jnlp is missing !?