Apache is receiving requests at port :80 and proxying them to Jetty at port :8080
The proxy server received an invalid response from an upstream server
The proxy server could not handle the request GET /.
My dilemma: Everything works fine normally (fast requests, few seconds or few tens of seconds long requests are processed ok). Problems occur when request processing takes long (few minutes?). 
If I issue request instead directly to Jetty at port :8080 the request is processed OK. So problem is likely to sit somewhere between Apache and Jetty where I am using mod_proxy. How to solve this? 
I have already tried some "tricks" related to KeepAlive settings, without luck. Here is my current configuration, any suggestions?
#keepalive Off                     ## I have tried this, does not help
#SetEnv force-proxy-request-1.0 1  ## I have tried this, does not help
#SetEnv proxy-nokeepalive 1        ## I have tried this, does not help
#SetEnv proxy-initial-not-pooled 1 ## I have tried this, does not help
KeepAlive 20                       ## I have tried this, does not help
KeepAliveTimeout 600               ## I have tried this, does not help
ProxyTimeout 600                   ## I have tried this, does not help
NameVirtualHost *:80
<VirtualHost _default_:80>
    ServerAdmin 
[email protected]
    ServerName www.mydomain.fi
    ServerAlias mydomain.fi mydomain.com mydomain www.mydomain.com
    ProxyRequests On
    ProxyVia On
    <Proxy *>
            Order deny,allow
            Allow from all
    </Proxy>
    ProxyRequests Off
    ProxyPass / http://www.mydomain.fi:8080/ retry=1 acquire=3000 timeout=600
    ProxyPassReverse / http://www.mydomain.fi:8080/
    RewriteEngine On
    RewriteCond %{SERVER_NAME} !^www\.mydomain\.fi
    RewriteRule /(.*) http://www.mydomain.fi/$1 [redirect=301L]
    ErrorLog /var/log/apache2/error.log
    # Possible values include: debug, info, notice, warn, error, crit,
    # alert, emerg.
    LogLevel warn
    CustomLog /var/log/apache2/access.log combined
    ServerSignature On
</VirtualHost>
Here is also the debug log from a failing request:
74.125.43.99 - - [29/Sep/2010:20:15:40 +0300] "GET /?wicket:bookmarkablePage=newWindow:com.mydomain.view.application.reports.SaveReportPage HTTP/1.1" 502 355 "https://www.mydomain.fi/?wicket:interface=:0:2:::" "Mozilla/5.0 (Windows; U; Windows NT 6.1; fi; rv:1.9.2.10) Gecko/20100914 Firefox/3.6.10"
[Wed Sep 29 20:20:40 2010] [error] [client 74.125.43.99] proxy: error reading status line from remote server www.mydomain.fi, referer: https://www.mydomain.fi/?wicket:interface=:0:2:::
[Wed Sep 29 20:20:40 2010] [error] [client 74.125.43.99] proxy: Error reading from remote server returned by /, referer: https://www.mydomain.fi/?wicket:interface=:0:2:::