The bug

While testing for MC-4544, I noticed the light flash isn't displayed at all now. Not sure about this, but it probably is not an intended change (at least it is not mentioned in the 1.13-pre2 changelog).

From Artist:

Fireworks use the index span between 72 and 191 for the big flash of the explosion, but that area is empty in the particles.png file (red square in the attachment). It was probably supposed to use the sprite bordered in orange (which would be the 36-87 square).

Fireworks also use one too many sprite in their trail/spark animation and they go down to index 159. You can't notice it at first because the index is empty in the original  texture. But if you fix the first error (by painting an explosion flash in the red square), you notice that the last sprite of the trail samples from that same flash square! (blue square). One error hiding the other .