Internal Employee's manager not getting change after transfer or Position change

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I was testing for the internal candidate selection process. Where I have noticed that the manager is not getting change base on position. So here we are using the position hierarchy concept.

Eg. Employee A is in Manager Position and the Manager's name is Z.

Employee A applied for Job of Senior manager and for that manager is Y. 

When employee A is selected for the position of senior manager and when HR doing the action of the position change.

Employee A manager still remain the same is Z.

Does anyone has noticed the same?