A dispenser facing down to drop boats into water fails to fire some of the time when triggered by a remote or adjacent redstone signal (from button, torch, lever). The dispenser will fire a few times or just once before stopping. Repeated attempts to fire fail for as long as more than a minute. Getting closer to the dispenser seems to help but not always.

Have been in creative and survival modes. World is flat and biome is plains. Another dispenser within a few blocks is facing sideways and has not misfired once when triggered by tripwire hook.

Perhaps the problem is with the orientation being down.