I've also just noted that the message was logged only when using google chrome. Just tried the page with IE as a test but the message wasn't logged.
I guess it's chrome that doesn't like mod_deflate. Maybe it's this
Does this happens with firefox?
Not sure how serious this, and I find it weird why the Apache docs don't have ANY info on this.
If it works with FF and IE then it's not serious, as chrome is still not widely adopted. Maybe that's the reason there is nothing on apache docs.
Let's hope google fixes the bug soon.