Wrong date on Multiheader and Hierarchical Grid


I try to make grid with multiheader column and hierarchical grid. I create multiheader column grid with razor helper and hierarchical grid from controller. But when I show date, it always -1 from data that I send. For example, data source send to browser with value /Date(1456765200000) but it shows as 29 Feb 2016.

If I remove a few lines about multicolumn header in grid, date shows correctly.

It happen when I use either Multicolumn Header Grid or normal grid child in Hierarchical Grid.

Is there any solution?