Put the summary of the bug you're having here
In 15w31a
What I expected to happen was...:
A Dispenser facing up was meant to be firing potion of harming and potion of poison arrows and single arrows should have been picked up.

What actually happened was...:
A Dispenser facing up was meant to be firing potion of harming and potion of poison arrows and fired whole stacks of arrows at the same time. Instead of the max 9x64 stacks of arrows it would fire a single arrow and come down as a stack of arrows of that type.

In 15w31b
Some normal arrows where sometimes fired from the dispenser instead of the potion effect ones.

Steps to Reproduce:
1.Place Dispenser with redstone blinker circuit
2.Turn on circuit
3.Fires arrows