I've had this bass since new and it's perfect for me in terms of playability and tone - especially the bottom end. Normally I play with both pups wide open and vary the tone pot as I need. However I've recently noticed that if I back off with either of the volumes then this affects the tone but only in the range from 12 back to 11 o'clock. In effect, "blending" the pups only works if one is at full volume and the other is between 11 and 12. Anything below 11 has no effect. Is this normal operation for this model or have I got a wiring anomaly?