It's a bug I found with the "LifeTime" dataTag.

When you use this command the firework doesn't explode:
/summon FireworksRocketEntity ~ ~2 ~ {LifeTime:0,FireworksItem:{id:401,Count:1,tag:{Fireworks:{Explosions:[

{Type:0,Flicker:0,Trail:0,Colors:[16711680,16740124,16771092],FadeColors:[16764784]}

]}}}}

You can change LifeTime to 200 (~10s) but it still doesn't work...