What I expected to happen was...:
If a block of wood has a fully grown cocoa bean on it, when the block is retracted by pistons more than one cocoa bean should drop.

What actually happened was...:
Only one cocoa bean ever drops.

Steps to Reproduce:
1. Construct the circuit as shown in the attached screenshot. There should be bonemeal in the hoppers.
2. Place a coca bean on the front of the wooden log.
3. Toggle the lever on and off again.
4. A number of cocoa beans (should) have dropped.
5. Place one of them on the now-extended log.
6. Toggle the lever.
7. Only one cocoa bean will drop.

This system works as expected (cocoa beans are successfully grown both times) in 1.7.4, so it (probably) isn't an issue with my admittedly-lacking redstone skills.