Here are the steps to reproduce on a Winter 13 sandbox:
Create the following VisualForce component called TestClickJackComponent:
<apex:component >
<!-- Begin Default Content REMOVE THIS -->
<h1>Congratulations</h1>
This is your new Component
<!-- End Default Content REMOVE THIS -->
</apex:component>
Create the following VisualForce page called TestClickJack:
<apex:page StandardController="Lead">
<!-- Begin Default Content REMOVE THIS -->
<h1>Congratulations</h1>
This is your new Page
<!-- End Default Content REMOVE THIS -->
<c:TestClickJackComponent />
</apex:page>
Add the page to your lead page layout. You'll see:
Congratulations This is your new Page Congratulations This is your new Component
Now go to Enable Setup-Security Controls – Session Settings and select Enable clickjack protection for non-setup customer Visualforce pages
Now you'll see:
URL No Longer Exists You have attempted to reach a URL that no longer exists on salesforce.com.
So, my question is - is this a bug? Or is it expected behavior with the new clickjacking protection?