cant split items into ststacksacs of 1

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here

What actually happened was...:
Describe what happened here

Steps to Reproduce:
1.first grab a stack of blocks and split them multiple times into 1 by right clicking.
2. it will return to the stack you split it from.
3. try not to break your monitor.