Unhandled exception caused by AssetBundle downloading in Unity 4.1.2

When my built project .exe terminated, there is an unhandled exception pops up. (WinXP SP3 32bit)

After a wee bit of investigation, the exception is an "Access Violation", and the culprit sits somewhere within CacheDownloadBuffers::~CacheDownloadBuffers() in this file: "c:\buildagent\work\7535de4ca26c26ac\platformdependent\commonwebplugin\unitywebstream.cpp" (according to "Unity.pdb", loaded into VS2008)

Turns out, any code that download AssetBundle from extern folder with WWW will cause this exception. Here's what I did (almost identical to the example in documentation):

 var www = new WWW(url);
 yield return www;
 Bundle = www.assetBundle;
 

...

 Bundle.Unload(false);
 Resources.UnloadAsset(Bundle);
 Bundle = null;

This issue seems to be Unity 4.1.2 exclusive. I tried the exact same thing in Unity 4.0.0, the program ended gracefully. Does anyone know a solution or workaround for it?

Thanks in advance!