I had a problem with some AJAX based web sites, after some debugging a figured out that problems comes caching proxy (squid3). The content of this web sites was always outdated and sometimes I get strange errors.
Disabling cache for a single domain or a list of predefined domains was a great solution in my case, here it is:
Configuration snippet from /etc/squid3/squid.conf:
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# Disable Cache for defined domains acl disable-dom-cache dstdomain "/etc/squid3/acls/no-cache.acl" cache deny disable-dom-cache
cat /etc/squid3/acls/no-cache.acl .vk.com
Very helpful. saved a lot of time.