What I expected to happen was:

The lower sand block falls, lands and then the upper sand block falls and lands on the other one

What actually happened was:

The lower sand block falls, lands and then the upper sand block falls and gets destroyed when touching the other one, you can see this in attachment2.png

Steps to Reproduce:
1. Build a construction like it is shown in attachment1.png (the pistons are sticky)
2. Activate both levers
3. Deactivate the upper lever and then deactivate the lower lever as fast as you can