I've noticed that when displaying the sidebar on a custom visuaforce page using <apex:page ... sidebar="true"> or omitting the sidebar parameter, that I can't collapse the sidebar.  I see the handles to collapse it but they don't do anything when clicked.  The collapse sidbebar setting is enabled in the User Interface customization in Setup and it collapses fine on standard Salesforce pages.  Am I doing something wrong or is this a "feature"?

Thanks in advance,
David