Bc2000 (for the BCF2000 & BCR2000)

Hi everyone, I have a BCR2000 for about 6 months. When I "spin" the push encoders in an attempt to change values very fast they don't respond as expected, sometimes only moving by a few values and in a very erratic fashion.  Is this because they are optical controls or does this sound like a fault.  All the push encoders perform in this way.  I have tried different settings for the encoders but get the same results including altering the acceleration settings through sysex.  If I move the encoder at a slower speed it operates as expected but was hoping to operate at speed with these controls.  

thanks
Alan