Hi Monica,
I am not sure which version of CA PPM you are using but I just tested in a CA PPM 15.4 version, and when you add Resource A as the Resource Manager of Resource B, Resource A automatically acquires the Resource Manager (Auto) access right for that specific resource instance (in this case, the instance is Resource B). Now when you again, change the Resource Manager field of Resource B to something else, the Resource Manager (Auto) access right gets removed from Resource A. And as he is not having any other administrative right(s), I can see that he is having Restricted License again.
So I am assuming that in your case, either the resource is having some other Admin/Edit rights or there must some other resource for which the Old RM is holding back the Resource Manager (Auto) access right. Try to check by clicking on that instance specific right, if you can see any other resource for which he is having that right. Hope that helps.
Regards,
Abhisek Dhar