ASP.NET AJAX - Script compression doesn't work in IE6

I try to enable compression in script resource handler in web.config file:

   1:  <system.web.extensions>

   2:      <scripting>

   3:          <scriptResourceHandler enableCompression="true" enableCaching="true" />

   4:      </scripting>

   5:  </system.web.extensions>

Analyzing the network traffic I discover that this works fine under Opera, Mozilla Firefox, IE7 but doesn't work under IE6. Response headers for Mozilla Firefox:

HTTP/1.1 200 OK
Content-Length: 23423
Expires: Mon, 11 Aug 2008 11:35:45 GMT
Date: Sun, 12 Aug 2007 11:35:45 GMT
Content-Type: application/x-javascript
Server: Microsoft-IIS/6.0
X-Powered-By: ASP.NET
X-AspNet-Version: 2.0.50727
Content-Encoding: gzip
Cache-Control: public
Last-Modified: Sat, 04 Aug 2007 12:23:19 GMT

Response headers for IE6:

HTTP/1.1 200 OK
Content-Length: 84019
Expires: Mon, 11 Aug 2008 11:44:23 GMT
Date: Sun, 12 Aug 2007 11:44:23 GMT
Content-Type: application/x-javascript
Server: Microsoft-IIS/6.0
X-Powered-By: ASP.NET
X-AspNet-Version: 2.0.50727
Cache-Control: public
Last-Modified: Sat, 04 Aug 2007 12:23:19 GMT

Can anybody explain this behavior of ASP.NET AJAX?