Hmm, seems like strange behavior. What are you trying to do with these keys? I'm assuming use the "media keys" to do play/pause, track fwd/back, etc.
I have all of those mapped to other keys, using MC's key assignment file. For example, <Command><up arrow> is Volume Up. <Command><down arrow> is Volume Down.
If you like the media keys, I'm not trying to change your mind. I just always found them to be in the "wrong place", so I did mappings that made sense to me.
Brian.