Dispenser constantly active while not directly receiving power

In order to deactivate a hopper above a dispenser while not powering the dispenser, I am powering a block adjacent to the hopper. For some reason the dispenser gets activated (only after it is powered once) as well, rendering it useless as it can't shoot any items (except for one when its being powered the first time). When the power to the block adjacent to the hopper is cut, on the first try the dispenser doesn't shoot and on the second+ it does.