Behavior of fired fireworks in double dispensers change depending on if it contains a firework star

When two double dispensers are stacked on top of each other (facing upwards) and firing a firework from the bottom dispenser, the behavior of where the firework explodes changes depending on if it contains a firework star or not.

Steps to reproduce

1. Place two dispensers facing upwards on top of each other

2. Place a firework (without a firework star) in the bottom dispenser

3. Power the bottom dispenser and observe where the firework shoots upwards

4. Place a firework (with a firework star) in the bottom dispenser

5. Power the bottom dispenser and observe that the firework explodes between the two dispensers

Expected behavior

It would be expected that the behavior of the different fireworks would be consistent with each other and that the firework would shoot upwards similar to the behavior of shooting items in the same system.

See attached 

for quick demo