Volume Control Problem

I am having some problem with my volume up and down command. I am using the global cache GC-100-12 to connect to my Pioneer SC-25 receiver through serial connection. When I press and hold the volume up or down button, the volume changes a few degrees and then stops or it stops for a moment and changes again. In other words it does not change the volume as smooth as it is suppose to be. Is there any possibility that the GC-100-12 is responding slowly when the volume is pressed and held, because when I am pressing the volume button one touch at a time, it works fine.