.Net SDK does not assign correctly access rights to a folder

We need to assign Full Control access level for a certain folder to one of our
user groups in .Net SDK code (C#). This code is supposed to do this task, and it was used
successfully in previous versions like BOXI R2:

SecurityInfo si = folder.SecurityInfo;
ObjectPrincipals ops = si.ObjectPrincipals;

ObjectPrincipal op = null;
op = ops.Add(principalID);
op.Role = cerole;
folder.Save();

In this code cerole represents enum CrystalDecisions.Enterprise.CeRole
and was checked with different values: FullControl, ViewOnDemand.
Regardless of used value, resulting access level, visible in CMC is "No
Access". Is it a bug in BO4? Does anybody know how to do it in BO4 .Net SDK?