Partially indexed but search for cache produces accurate result. Why?

Contradictory results

[Talar]

My website is only partially indexed (no description, no cache) therefore it doesn’t appear under any keyword search, however if I do a cache search (cache:mywebsite.com) I always find it and is fairly recent (currently Mar/04). It has been like that for 6 weeks. Why is this happening?

[tedster]

Can only guess, but it sounds like a back end mash-up at Google -- possibly a difference in data centers.