IE start page with group policy

I tried to set the start page of IE by the group policy. This does not function.
The settings in the Home Page area on the General tab in the Internet Options dialog box appear dimmed but the value does not change.
Gpotool tells “no error”. Gpresult show that the correct value for the policy is downloaded and regedit sho the good value too in HKCU\Software\Policies\Microsoft\Internet Explorer\Control Panel. But the value in HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings is not adapted.
What could append ?