I have had this same issue with my Logitech Elite keyboard. Volume slider, mute, and playback buttons work fine out of the box without the use of Logitech's iTouch (keyboard) software on Windows XP SP2. When ApexDC++ window is in focus, the volume slider and mute buttons are unresponsive. It's not a big deal at all, but I've noticed this behaviour for quite some time and I believe it is the same with StrongDC++. Possibly can be fixed by installing Logitech's software, but I'm not much to care for their software, and Girder takes care of these things with much more extensive customization.
