Your browser's cache settings must be set to "Compare the page to the cache - Each visit to the page".

For Internet Explorer on a PC:

In your browser window, click Tools and choose Internet Options. Click on the Settings button next to "Temporary Internet files" Make sure that "Every visit to the page" is selected and click OK.

For Internet Explorer on a Mac:

In your browser window, click Edit and choose Preferences. When the Preferences window opens choose Advanced. Make sure the button next to "Always" is chosen, then click OK.

For Netscape on a PC or Mac:

In your browser window, click on Edit. From the drop-down menu, select Preferences. Click the "+" sign next to Advanced. Highlight Cache. Make sure that the "Every time" radio button is selected and click OK.