Grouping shows two same rows (if initially grouped)

http://plnkr.co/edit/EbmEMgrw8GCyHakajrKC?p=preview Here is the sample, the problem is, when I set data like this var data = [ {"A":"11","B":"12","sum":1}, {"A":"11","B":"122","sum":2}, {"A":"11","B":"123","sum":3}, {"A":"112","B":"127","sum":60000}, {"A":"11","B":"129","sum":3015}, ]; it shows A B sum 11(3) 6 112(1) 60000 11(3) 6

so I compared my data with the sample grouping , I found when I set data like this var data = [ {"A":"11","B":"12","sum":1}, {"A":"11","B":"122","sum":2}, {"A":"11","B":"123","sum":3}, {"A":"11","B":"129","sum":3015}, {"A":"112","B":"127","sum":60000}, ];

it works fine