Comment 7 for bug 219914

According to the Debian bug, enabling the disk_cache module on upgrade is the right thing to do. The proxy.load file in dapper loads mod_disk_cache. Not enabling it on upgrade would break existing system (as reported in the debian bug).

However, the apache2.2 package comes with disk caching enabled by default as of 2.2.4-2:

  * Disk caching is now enabled by default if mod_disk_cache is enabled. If
    you don't want to use disk caching, check that mod_disk_cache is disabled
    (it was enabled automatically by previous versions when mod_proxy was
    enabled). In this case, you might also want to remove any cache files from
    /var/cache/apache2/mod_disk_cache .

    To ensure that the disk cache does not grow indefinitely, htcacheclean is
    now started when mod_disk_cache is enabled. The details can be configured
    in /etc/default/apache2 .

This is done by using "EnableCache disk /" in disk_cache.conf (the same applies to mem_cache.conf). Removing this directive would not enable caching of / by default, but disk_cache would still be loaded if the proxy module was enabled in dapper. That way existing configurations using disk_cache won't break (mod_disk_cache is loaded), but existing configuration not using disk_cache won't have caching turned on by default.