Click/Tap in Modal also executed in page "underneath"

We use a modal to pick a value from a list.
The page which calls the modal contains a few sliders and buttons.
If the user clicks/taps in modal to pick a value, the click/tap is also “transmitted” to the page below.

This means, that if the user happens click/tap in modal in a region of the screen where the calling page contains a button or slider, the button/slider action is called, too.

In the example, if the user clicks/taps on the item “a” (a desc) the red button below will be executed after picking the item.

Is this a bug? or can we prevent the click being transmitted?