Grid does not scroll down with key down

Take this example of flexmonster https://jsfiddle.net/flexmonster/rkprvhhs/ (It is first demo from flexmonster website).
By default, I am able to see rows till September. 
Click on any month name and start pressing down arrow one by one(do not keep it pressed).
Highlighted cell moves down as long as it is in view port, after that view is not scrolled to that point. It starts scrolling after few key presses.
In big data sets having lot of rows or nested rows, it appears as if view is not scrolling at all, it can be reproduced by adding few more fields as rows.