You will be better off experiencing this in portrait mode, as splitActionBarWhenNarrow is clearly intended for narrow (i.e. portrait) orientations.
This project is designed specifically - when in landscape mode, your vertical real estate is more limited, so it makes sense to maximize the large width of one action bar, and not take up twice as much space (top and bottom). Although the Ethan link provides will lead you to some kind of custom implementation, I suggest revising the design to follow Android design patterns as much as possible. Reject if you have a really good reason, of course.