Page Cache Enabled but no caching

I can see the cache page is generated in wp-content/w3tc/pgcache
However the debug info is saying the page is not cached.
What can be wrong?
Thanks

Here is the debug info:

<!-- W3 Total Cache: Page cache debug info:
Engine:             disk (enhanced)
Cache key:          contact-me/_index.html.gzip
Caching:            enabled
Status:             not cached
Creation Time:      0.370s
Header info:
Content-Type:       text/html; charset=UTF-8
Last-Modified:      Thu, 18 Aug 2011 14:35:08 GMT
Vary:               Accept-Encoding, Cookie
Expires:            Fri, 19 Aug 2011 00:35:08 GMT
Pragma:             public
Cache-Control:      max-age=36000, public, must-revalidate, proxy-revalidate
Etag:               4c9a18236a8fca767ae23fd727663226
X-Powered-By:       W3 Total Cache/0.9.2.3
Content-Encoding:   gzip
-->

Could anyone kindly give me some pointers?