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The answer to this is likely _CACHE_ either way, when you step back, Mr. Cache wakes up with his supermutant memory which remembers that pages, and instead of updating it again he let's you read his mind.
The only thing I can think of, assuming you've addressed the point that syranide mentioned, is that you aren't trying to delete the cookie with the same arguments that you set it with. Now, I know that in the snippets you provided argument count was the same, but maybe in your code it's not ?