If there is more than one bucket in a dispenser the source blocks may end up overwriting each other.

What I expected to happen
If there is a source block of either water or lava in front of the dispenser and an empty bucket in the dispenser there is a 100% chance of the block being put into the bucket.

What actually happened
There is still an equal chance of any of the slots in the dispenser being used. (e.g water outside, empty bucket and lava bucket inside => 50/50 chance either will be used, instead of a 100% chance the water block being put into the bucket.)

Steps to Reproduce
1.) Put an empty bucket and lava bucket in a dispenser.
2.) Put a water source block in front of dispenser.
3.) Power the dispenser.
4.) Observe the random nature of the choice of dispensed item.

Windows 7, not sure about the Java.

(P.S This bug is stopping the creation of probability devices that completely outclass any old cactus based probability generators, allowing almost any probability to made accurately.)