Item Stacks dont seperate?

Put the summary of the bug you're having here

What I expected to happen was...:
The right click button should make drop half or one of the items into seperate stacks

What actually happened was...:
The item remains in one stack, and cannot be seperated, except with very complex procedures.

Steps to Reproduce:
1. Get a stack of items
2. Go in your inventory,chest,crafting table ,etc.
3. Select your item stack and try to seperate them.