Issue in report contacts grouping city wise

I found a issue in report created for contacts grouped city wise in sugarcrm 6.5,

I have created a report for contact list city wise, have added city in group "Group By: City" have also added same field in display column(Display Columns: Name, Email Address, Account Name, Designation, City), 

Same city field is used in grouping and display columns, any suggestions ?

In result I found 

City = None, Count = 8

and in entries under this None group have city names in few and empty in few, same for City = Mumbai, some entries have city name as Mumbai and for some it is blank.