Apache is not sending 304 response (if mod_deflate and AddOutputFilterByType is enabled)
This is a known bug in Apache. See Apache bug #45023, and summary of Apache 304 etags and mod_deflate. Rebuilding from svn will fix the issue. The resolution was to revert the change that appended “-gzip” to the etag. However, there are associated HTTP compliance problems. If you can’t rebuild Apache, there is a suggested … Read more