According to http://doc.trolltech.com/3.3/qkeyevent.html#details "Key events for multi media keys are ignored by default. You should call QKeyEvent::accept() if your widget handles those events."
Currently, LyX calls accept() for everything, so multimedia keys are undesirably blocked: http://www.lyx.org/trac/ticket/6043 My patch http://www.lyx.org/trac/attachment/ticket/6043/multimediakeys.diff simply changes "void processKeySym" to "bool processKeySym", and returns false whenever it encounters an "Unknown function". That return value then determines whether to call accept() or ignore(). Rock on, -Ben
