Isolation Mode semantics for GPO v registry

Hi,

I think I understand the semantics of isolation mode, however when I set a web app default home page to be http://url.com, when I install the webapp and have it fully locked down with no address bar, context menu etc.  However it picks up the GPO default URL and goes to that site instead of the one that I have set in the registry as isolation full.  My understanding (could be wrong) is that GPO overrides, but is this the case in isolation full as well and if so is there a way around this?

Thanks,

isolation_full HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main

  Value=Start Page

  REG_SZ~http://url.com#2300