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If it's the same as previous versions, you might be able to fix that in Internet Settings. It offers several options for "Check for new version of a page" as described at How Internet Explorer cache settings affect Web browsing (I know that talks about IE 4 and 5, but they've not fixed it yet). Try setting it to the "Every visit" option.
I don't know what the IE9 default is, or if it's supposed to respect the existing settings, but IIRC the default on previous versions was "Automatically" which translates to "According to a well-hidden set of rules which lead to results that aren't what anybody would either expect or desire".