Two headline tests:
headline/URLBugs/4422857
headline/URLBugs/jarFile
passed on JDK 1.5.0 u12 b01 but faild on JDK 1.5.0 u12 b02 with exception:
java.lang.RuntimeException: java.security.AccessControlException: access denied (java.net.SocketPermission sqeweb.sfbay.sun.com resolve)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:904)
        at sun.net.www.protocol.http.HttpURLConnection.getHeaderField(HttpURLConnection.java:1941)
        at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:376)
        at sun.applet.AppletClassLoader.getBytes(AppletClassLoader.java:269)
        at sun.applet.AppletClassLoader.access$100(AppletClassLoader.java:44)
        at sun.applet.AppletClassLoader$1.run(AppletClassLoader.java:158)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.applet.AppletClassLoader.findClass(AppletClassLoader.java:155)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at sun.applet.AppletClassLoader.loadClass(AppletClassLoader.java:119)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
        at sun.applet.AppletClassLoader.loadCode(AppletClassLoader.java:591)
        at sun.applet.AppletPanel.createApplet(AppletPanel.java:722)
        at sun.applet.AppletPanel.runLoader(AppletPanel.java:651)
        at sun.applet.AppletPanel.run(AppletPanel.java:325)
        at java.lang.Thread.run(Thread.java:595)
Caused by: java.security.AccessControlException: access denied (java.net.SocketPermission sqeweb.sfbay.sun.com resolve)
        at java.security.AccessControlContext.checkPermission(AccessControlContext.java:264)
        at java.security.AccessController.checkPermission(AccessController.java:427)
        at java.lang.SecurityManager.checkPermission(SecurityManager.java:532)
        at java.lang.SecurityManager.checkConnect(SecurityManager.java:1031)
        at sun.net.www.http.HttpClient.New(HttpClient.java:308)
        at sun.net.www.http.HttpClient.New(HttpClient.java:316)
        at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:813)
        at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:765)
        at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:690)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:934)
        at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:367)
        ... 13 more

Test was performed on "tezro.russia.sun.com"
Results located in
/export/home/JQA/ts150/security/root.Linux.i386/jarFile on machine tezro.russia.sun.com
Steps for reproducing see in comments.

May be this issue relaited with fix to 6509141.