DDJ-800 "beat sync" button light

When you switch on the DDJ-800 there is a dimmed light in both "beat sync" and "key sync" button so you can see them in the dark.
But when you start rekordbox the light in "beat sync" goes out.
So it's all dark ("key sync" still has a dimmed light).
Why?  Most other keys have a dimmed light when not active.