I've got a keyboard with a row of buttons that are supposed to do things like control the system volume and web browser et al.

Thanks to xev, for the first time ever I've got them all working.

Except for the "Next" and "Previous" keys, which I've bound to xmms controls.

I've set them to "xmms -f" and "xmms -r", which the man page says is the right thing to do. But when I press the keys, instead of skipping forward or back ONE track, it skips an entirely random number. Sometimes forward, sometimes backward.

Everything else works - I can control my alsa settings with the Volume buttons, I can control my browser with the Back & Forward buttons, I can make xmms play & pause. I just can't move one track forward or one track back.

Any ideas?

I bet your random button is checked in xmms. Sometimes hard to see infancy skins. Change to default xmms skins and see if random is checked.