The evaluation of the "alert()" function in a proxy.pac file stopped 
working beginning with 6u10. As a result the whole proxy.pac file fails
to get evaluated.

The problem is strictly reproducible using the following experimental 
setup:

1. Use IE6 on Windows XP SP2
2. configure the use of an automatic proxy file:
IE6 -> Tools -> Internet Options... -> Connections -> LAN Settings... ->
Use automatic configuration script

The following proxy.pac file was used:

 ---------------------------------
 function FindProxyForURL(url, host)
 {
  alert("hello world");
  return "PROXY webcache:8080";
 }
 ---------------------------------

3. Start IE6 and start a Java applet from the Internet.
 Start the Java Console window in order to verify which http proxy
 was used.
 
4. Observed behavior
--------------------
4.1  1.5.0_17
-------------
 The alert window "hello world" pops up twice:

 Microsoft Internet Explorer
       hello world
           OK

 It appears that the proxy.pac file is evaluated twice.
 The proxy is correctly set to "webcache:8080".
 Everything is fine.

4.2  1.6.0_07
-------------
 The alert window "hello world" pops up once.
 It appears that the proxy.pac file is evaluated only once.
 The proxy is correctly set to "webcache:8080".
 Everything is fine.

4.3  1.6.0_10
-------------
  The alert window "hello world" is not shown. Instead the
  following error window is shown:

 Microsoft JScript runtime error 
       Object expected
         OK-button

 This error window is shown twice, suggesting that the proxy.pac 
 file is evaluated twice.
 The proxy is set to "DIRECT", which shows that the proxy.pac 
 cannot be parsed as a consequence.
 This observed behavior is identical both with New Java Plug-in and 
 Classic Java Plug-in.

4.4  1.6.0_11
-------------
 behaves identically to 1.6.0_10