Despite freshing pages numerous times, Google keeps reverting to very ancient caches for pages they don't crawl constantly, as old as August. December 8th is completely normal, as the fresh caches always fade away afer a couple days. You will keep reverting back to December 8th until they replace that cache with a newer one, or they start freshing/crawling your homepage every day.
Thanks for the comments. It is a bit weird, in that the Googlebot crawls my site 3-5 times per week. It was just that one day that the cache was a few weeks old. Naturally today, it is back to being current.
usually when that happens it is during a "google dance", and the databases roll back to some older cache before a new cache sets in. will take until a new cache is done on that page to stop (depends on the pagerank of the page in cache speed).