[Plugin: W3 Total Cache] Garbage Collection Is not Working / Stale Pages

Garbage Collection is set to 3600 seconds. It is not purging posts. I ran 2 tests to come to this conclusion:

Test 1) *note I have gzip disabled
I edited the _index.html file created for a specific post in /w3tc/pgcache/post-title/ directory. I added a small line in it. I view the post in a different browser (not logged into WP) and I see the edited line. After 3600 seconds I check again, it still showing the same. I clear all browser cache and check, still same. I check _index.html and it’s still the same.

Test 2) I check with HTTP Headers. *note 3600 seconds is 1 hour*
After flushing cache and visiting the page for first time I see HTTP Headers as follows:
– current date
– max-age=3585, max-age=3600 (this means the page is 15 seconds old – it expires when 3585 comes to 0)
– Expires date (which is the time it will be when above max-age is 0, so basically about 1 hour from now)

1 hour later I refresh the page and check HTTP Headers again. I see the following:
– current date ( more than 1 hour has passed )
– no-cache, max-age=3600 (I think this tells the browser to NOT cache this page)
– Expires date (still same date as before – the current date has already past the expires date)
*Note i refreshed browser cache and checked, same values for above – only difference is current date changes.

Screenshot: http://i.imgur.com/yG6hy.jpg

My specs:
Latest WP and stable W3TC
Nginx server – I added config rules that were outputted by w3tc in file nginx.conf

Pages are purged if I manually flush w3tc or update the post.

http://wordpress.org/extend/plugins/w3-total-cache/