Try adding a slider group number and see if that helps. My settings look like this:

*Slider "Winamp Seek" $sliderx$ $slidery$ $sliderbtnoff$ ampsliderBGT.bmp SlideRingT.bmp HATI#1 [WinAmp] 0
*Slider "Winamp Volume" $sliderx$ $slidery+9$ $sliderbtnoff$ ampsliderBGB.bmp SlideRingB.bmp HATI#1 [VOLUME] W
*Slider "Main Volume" $slMainX$ $slMainY$ 0 sliderBGL.bmp SlideringL.bmp VTAB#0 [VOLUME] 0
*Slider "Wave Volume" $slWaveX$ $slWaveY$ 0 sliderBGR.bmp SlideringR.bmp VTAB#0 [VOLUME] 1