The fix:

Mac OS X Server 10: Web service uses ports 80 and 16080 by default

How to enable or disable Performance Cache

Click to select/deselect the checkbox for 'Enable performance cache' in the Server Admin application. This setting is located in the General pane of the Web Service module of Server Admin.

Except that in 10.4, it's found under Sites -- double-click the site you're changing, then the "Options" tab for that site. Checkbox est la.