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I do sometimes tend to mis-read questions on SO and post completely pointless and stupid answers. So when I realize what I've done, I delete the post and refresh the page, to have it disappear.
But, sometimes, the post does not like to vanish. And it stays there, for a long time, giving me the option to "undelete" it.
I don't think it has anything to do with cache, as I'm sure the cache is updated within 2 months, right? - I've just come across one of my old (about 2 months old) post, that I deleted two months ago, and its still there...
I know the post is only visible to me, but I don't know why some don't go for good, and some do.
Also, if the post affected my rep (the post got any down/up-votes), my reputation does not get re-calculated as it usually does on posts that disappear for good.
Why is this? Is there a specific cause for some posts to not be deleted for good?