In this case, the issue could be related to the side from which you are inserting the records or making the relationship. For example if you have User1 that has rights on User2 and you are trying User1.ManagedUsers.Add(User2) and having the problem described, you can try the other way around: User2.ManagedBy.Add(User1). The idea is to change the direction you are adding to between the Source and the Target. However this is a workaround, we will have to have a deeper look into the issue as having the Managed setting set on both sides should synchronize the Source and Target collections thus, this problem should not be present.
Please excuse us for any inconvenience this might cause you, if you have any further questions, please do not hesitate to get back to us.
the Telerik team
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