jnordstrom I noticed this exact same thing in my logs you can either. change deflate.conf to look like this and the error will still be there only for some hosts.

<IFMODULE mod_deflate.c>
# Commented out filter below to disable default compression to allow some 
# virtual hosts to have no compression. 
# AddOutputFilterByType DEFLATE text/html text/plain text/xml 
</IFMODULE>

Another alternative is to just edit the rule file and ditch the warning. I'm busy contemplating which one to do myself right now.