Using ZCS 8.0.2 (single host), I have installed apache and configured it as a reverse proxy in order to install other Web application on the same machine:
SSLProxyEngine on
# 7443 = zimbraMailSSLPort
ProxyPass / https://machine.domain.com:7443/
ProxyPassReverse / https://machine.domain.com:7443/

This works, but from time to time, I get these errors in apache logs:

[Thu Feb 21 12:09:01 2013] [error] [client a.b.c.d] (70007)The timeout specified has expired: proxy: error reading status line from remote server machine.domain.com
[Thu Feb 21 12:09:01 2013] [error] [client a.b.c.d] proxy: Error reading from remote server returned by /Microsoft-Server-ActiveSync

I saw this thread:
and tried using:

SetEnv force-proxy-request-1.0 1
SetEnv proxy-nokeepalive 1

but this does not work for me (the errors still occur).
Thanks in advance,