Duplicate rows are formed due to how Microsoft interprets the parameter -Identity. This parameter is not set as unambiguous, and as such it not only searches for matches in Identity, it also search for matches in Alias, SamAccountName, EMailAdresses, LegacyExchnageDN and UserPrincipalName.
An incident has been opened with Microsoft but Microsoft has rejected any change request related to this parameter. As such additional code around the Cmdlets needed to be written to address these shortcomings.
Enhancement Request 30269 has been logged and changes for this Enhancement has already been implemented in v8.1.1.
However there will be no hotfixes available for earlier versions for this Enhancement. Reason is this Enhancement requires a very high percentage of cmdlets to be rebuilt towards Exchange Online and just can't be provided as a hotfix.