This is a common problem noted on inspections.
In a tub/shower combination the tub spout has a diverter valve attached to the tub spout. When shower operation is required this valve is pulled up thereby sending the water up to the shower head. As this valve wears out over time it will not completely shut off the water and divert it to the shower head. This will cause the water pressure at the shower head to be low and water to pour out of the tub spout, as you can see in the image.
It is an easy replacement/fix by a homeowner or a qualified plumbing contractor that will assure full water flow to the shower head.
