Unable to push IE compatibility view list

The GPO is not working for me.  I am using:

Computer or User Configuration-> Policies-> Administrative Templates-> Windows Components ->Internet Explorer -> Compatibility View -> Use Policy List of Internet Explorer 7 sites

The format I am using for the list is:
stackoverflow.com
etc

I have pushed to client PCs (winXP with IE8, and win7 with IE10), and have verified via rsop.msc that the setting is correctly pushed.  I also verified the regkey is getting pushed to Software\Policies\Microsoft\Internet Explorer\BrowserEmulation\PolicyList\

What doesn't work: IE does not display sites in compat view.  I am checking by loading the web site, then inspecting the compat view icon next to the address bar, and bringing up the f12 developer window and checking the browser mode label.

Thanks,
Jaime