Comment 7 for bug 223412

Same issue...
Clean install of kubuntu intrepid i386 and amarok 2 instead of 1.4, with instructions from kubuntu.org.
Play/Pause button works as global shortcut, but "Media Next" and "Media Previous" only work as local shortcut. If used as global, they do nothing.

Using other key combination like "Meta + U" also works as global for changing music

.kde/share/config/kglobalshortcutsrc file looks fine after changes:

[amarok]
_k_friendly_name=Amarok
decreaseVolume=,Meta+-,Diminuir Volume
increaseVolume=Meta++,Meta++,Aumentar Volume
loveTrack=Meta+L,Meta+L,Adorar Faixa Atual
mute=Meta+M,Meta+M,Mudo
next=Media Next,Meta+B,
play_pause=Media Play,Meta+C,Reproduzir/Pausar
playlist_add=Meta+A,Meta+A,Ad&icionar Arquivos...
prev=Media Previous,Meta+Z,Faixa Anterior
rate1=Meta+1,Meta+1,Avaliar a Faixa Atual: 1