Apache & IIS 7.5 as reverse proxy incorrect response header value

On a Windows 2008 R2 IIS 7.5 with an ARR and URL Rewrite running on port 80th On the same server Apache on port 10000 is running (had not taken 8080 by design). IIS forwards all inquiry going on / cp1 on to Apache (reverse proxy).

On the Apache run by many Ajax requests to the database. Should such requests more than 5 seconds, I get the following message from IIS:

Fehlerzusammenfassung
HTTP-Fehler 502.3 - Bad Gateway
Der Server lieferte eine ungültige oder unbekannte Rückmeldung.
Ausführliche Fehlerinformationen
Modul   ApplicationRequestRouting
Benachrichtigung    ExecuteRequestHandler
Handler ApplicationRequestRoutingHandler
Fehlercode  0x80072f78
Angeforderte URL    http://win2008r2iis:80/cp1/index.pl
Physikalischer Pfad C:\inetpub\wwwroot\cp1\index.pl
Anmeldemethode  Anonym
Angemeldeter Benutzer   Anonym

The response header indicates to me now as follows:

Pragma: no-cache
Date: Thu, 08 Jan 2015 10:27:00 GMT
Server: Microsoft-IIS/7.5
X-Powered-By: ARR/2.5, ASP.NET
Content-Type: text/html; charset=utf-8
Cache-Control: private
Content-Disposition: inline;
Keep-Alive: timeout=5, max=100
Content-Length: 5323
Expires: Tue, 1 Jan 1980 12:00:00 GMT

The problem is stated in the Keep-Alive header 5 seconds. According to the web.config but 1 minute are set as timeout:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
        <handlers>
            <remove name="Perl" />
            <remove name="ActiveState Perl for *.pl" />
            <remove name="PerlEx" />
        </handlers>
        <staticContent>
            <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="1.00:00:00" />
        </staticContent>
        <httpProtocol allowKeepAlive="true" />
    </system.webServer>
   <system.applicationHost>
      <webLimits connectionTimeout="00:01:00" />
   </system.applicationHost>
</configuration>

In the ARR cache settings is entered as the value is 120 seconds.