Key mapping puzzler

Here’s a keymap puzzler.

The following does not seem to work:

Code:
<VideoOSD>
    <keyboard>
      <next_track>PlayerControl(SmallSkipForward)</next_track>
      <prev_track>PlayerControl(SmallSkipBackward)</prev_track>
    </keyboard>
  </VideoOSD>
  <FullScreenVideo>
    <keyboard>
      <next_track>PlayerControl(SmallSkipForward)</next_track>
      <prev_track>PlayerControl(SmallSkipBackward)</prev_track>
    </keyboard>
  </FullScreenVideo>

There are no keymap parsing errors in the log. The next and prev track keys go through to skip next/prev as mapped in the system keymap.

If I substitute some other keys for next/prev track, they work. Other media keys (like play/pause) also work.
If I map next and prev track in some other window, they work there.
Those particular keys just can’t be mapped in the video window. Any ideas why?