I am using Tomcat to compress my HTML content like this:
Perhaps the compression Tomcat is referring to isn't gzip? It's a stab in the dark, but it might relate to white-space compression, or line trimming.
I would imagine Tomcat would be a bit more explicit in this regard (here's hoping).
We have the gzip filter mentioned by duffmo running in our application, the web.xml looks something like this:
App-Web
GZIPFilter
weblogicx.servlet.gzip.filter.GZIPFilter
[snip]