UPD mapping after change in Users AD Logon Name

We have a Win2012R2 based RDS Session Host Farm with multiple RDS Session host & a couple of collections. Off course we also have RDWA NLB Farm, File Server Cluster for UPD store, RDSB, RDLic etc.

We believe that if we change the Users AD Logon Name, it should still load the same UPD when the users log's onto the RDS environment, as UPD's are mapped with users Domain SID'd rather than User Logon Name.

But what we actually see is that a new UPD is created for a AD Users if his AD Logon Name is changed.

This behavior is strange and we seek help if anyone can put more light.