Unable to Restrict delegation to users outside of the business unit

Summary:

Content (please ensure you mask any confidential information):

While assigning delegation, a particular user is able to search employees of other business unit as well. We want to restrict this functionality, such that the said user should not be able to search other users of other business units and only users of his business unit should be visible to select for delegation.

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):