I have a problem with water coming out of my tub spout whenever the shower is being used, what causes this and how do you fix it

If you have a three valve faucet set then it's because the center valve that controls the flow from your tub spout to your shower head needs replaced. If you have a two valve set with the pull up stopper in the tub faucet then the stopper is either old, dried out, and pieces broken off it or just plain worn out. In that occasion I believe you'll need to replace the spout assembly with the stopper installed in it. I don't believe you can just change the stopper on most models. If you have the first and have to change the valve I'll give you some advice to save you a lot of time. Turn off the water supply to your house, meter box is easiest method, then take the valve out and take it with you to the hardware store when you go to get the replacement. There are so many different sizes and models by brand that you can waste a lot of time and trips if you don't. Hope this helps.