I have 64 dispensers set up with a water bucket inside. These are all hooked up to separate buttons with redstone dust. All but one work as intended. When I push the button once they power and spit out water. I push the button a second time and they suck the water back in. The one that doesn't work refuses to suck the water back in. If I just put in two items (instead of the water bucket) the first will shoot out but the second will not so I do not think it is dependent on what is in the dispenser.

Now it gets weirder. If I power the dispenser from 1 block away it works every time. If the redstone line is two blocks away it stops working on the second push. Happens regardless of power source (redstone torch, lever, button, redstone block).

If I get into this state again I can also fix it by forcing a block update on any block next to the dispenser and then powering it again.

I've seen this only twice on my server and it makes no sense.

Forum posts seem to have similar issues:
http://www.minecraftforum.net/topic/1908884-unreliable-dispensers/
http://www.minecraftforum.net/topic/1735103-dispenser-issue-with-multiplayer-since-15/