addWizardPageItem doesn't work with all default pages

I am trying to add a checkbox on the ready page of the uninstaller to ask the user if he want his settings files removed.

The following code have an effect on the ready page of the installer but not on the uninstaller:

installer.addWizardPageItem(component, "DeleteSettingsCheckBoxForm", QInstaller.ReadyForInstallation);

I linked two captures, I am expecting to have the checkbox on both.

PS: I also tried to put the checkbox on the introduction page without success (for installer and uninstaller)