I don't know if this helps, but I've found that if you have a mandatory profile and apply Group Policy, the Group Policy will not apply unless the user is an administrator on the local computer. GPResult will say that it applied the policy, but the settings will not apply.
Related to this, I've also found that if the profile that you move to the default user on a local computer had a Group Policy applied to it(domain or local), then the policy will continue to apply to any profile that gets created from the default user, and GPResult will never show it being applied! I've made a point for the technicians to only copy the local administrator's profile (no domain GPOs) before any local GPO is created if they want to tweak the default user profile settings. Otherwise we end up with "ghost" group policy settings being applied.
Maybe what you're experiencing is related to either of those situations.