Navigation issue with keyboard up and down key.

when using up/down arrow and enter to navigate, sometimes cursor skips a cell when hitting the arrow key just once. And it becomes non-editing when the cell navigates to is out of the visible area.

it becomes non editable in up and down of last displayed row (Like 10 rows displays at a time so after 10 rows when we down keypress then it becomes non editable and sometimes it skips row.)

plunker : http://plnkr.co/edit/WizlYTzwdif3Exp1pTDT?p=preview