Suppress the up/down arrows from making a selection in a SELECT list

I've got a SELECT list that I want to suppress - disallow - the use of the arrow keys as selectors for the values in the SELECT list.

Those arrows are being used by a jQuery SlickGrid to move up and down in the grid - so having the SELECT list values change at the same time is really nasty.

I don't see why that should be happening, unless both the slickgrid and the SELECT have focus at the same time? I'm not even sure if that's possible...