I have water coming out of the faucet and the shower at the same time when handle is in between hot and cold water positions. Any ideas?

More details pleas,
Single handle? What brand? Is the diverter on the spout or in the valve? Did it ever work right or has this been ongoing? How many inches between the shower head and the valve? Pump or city water. Do you know how much water pressure your house has? Back to you, Tom