What happens: Pistons sharing the same clock will activate at different timings from one another. 

To reproduce:

1. Create a fast redstone clock (eg. observer clock)
2. Connect a line of redstone from an output of the clock
3. Place pistons connecting to the line

Sometimes, two adjacent pistons will fire in two different ticks, it doesn't always work (as seen in the video)

What should happen: No matter when the piston is placed, it is synchronized with every piston sharing the same redstone input.