The shower head in the master bath sometimes leaks when the toilet in the same area is flushed. Why?

When the water is turned off to a shower hear a large amount of wate rwill stay in the head if the head is positioned right, turned down is the most probable position for it to hole water. Sometimesd theis water can be released by you hitting the shower head. So I suppose that the flushing of the commode is just enough distrubance in the water lines to make the water come out of the head just like hitting it would be.