Your browser is caching those pages and probably other pages on the site too aggressively. You need to set your browser to always fetch the page every time there is a new one.
If you're using IE 7 on Windows here is how to fix the problem:
go 'Tools -> Internet Options: General Tab
Under 'Browsing history' Click the 'Settings' Button
Make sure that the top radio button 'Every visit to the page' is selected.
Click OK
Click 'Delete...'
In 'Temporary Internet Files', Click 'Delete files...'
Click 'Yes'
Click Close
Click OK
If you're using IE 5 and 6 on Windows here is how to fix the problem:
go 'Tools -> Internet Options: Middle pane 'Temporary internet files'
Click the 'Settings...' Button
Make sure that the top radio button 'Every visit to the page' is selected.
Click OK
Click 'Delete Files...'
Click OK
Click OK
Also, make sure that your computer's day and time are accurate so that your browser knows when to expire pages from it's cache at the right time. Clicking the refresh/reload page button on your browser should help.
If all of the above does not help that could mean that your ISP is using a proxy server and that there's a problem with their configuration.