Gold pressure plates and Iron pressure plates doesn't work with the same entity. Only with diferent, is this a bug?

What I expected to happen was...:
In 1.6.4, as you putting one type of entittie (e.g; 18 carrots) the signal is growing if you putting more entities of the same type.

What actually happened was...:
The Gold and Iron pressure plates only send one signal of redstone with the same type of entittie, either more or less, sends the same signal. (1)

Steps to Reproduce:
1. Put in inventory a lot of any item (32 for example)
2. Drop it in the pressure (Gold, for example)
3. The signal doesn't grow, only sends 1 signal of redstone.
4. Now put in inventory one item.
5. Drop it in the pressure
6. It sends the same signal as before.