If site is in the index, why is the cache empty?

[phpmaven]

My site has taken a hammering in the recent update, and I noticed something unusual when I was researching some of the pages affected. Just as an example:

Page used to rank in top 10 but now has dropped to 200+

When you use the toolbar to look up the cache it says there is no cache for that page.

When you do a search on the url it says that there is no info for that url.

However, if you search for some unique text on that page it will come up in the serps. Also if you click the cache link in the serp, it shows you the cache.

So the page is in the index and yet the toolbar shows no cache and a search for the url says that there is no info, so I'm a bit confused.

Any insight would be appreciated.