I'm commenting here since another similar bug was resolved as "Won't fix" because of this one: if I am doing it correctly, the problem persists. This is the command I used:

/summon Fireball ~1 ~ ~ {ExplosionPower:5,direction:[0.0,0.0,0.0],power:[0.0,0.0,0.0]}

It still has jittery movement, snapshot 15w51b.

The problem was that the power tags were not saved. Now they are saved. In commands they NEED to be set up properly, otherwise it will cause jittery movement. That is not a bug.

No new NBT tags added and behavior seems unchanged as of 15w47b.

Reopened, please re-test next snapshot.

Actually not yet fixed in 15w46a

I summoned SmallFireballs in 15w45a and 15w46a in both versions, and no new NBT tags were added (at least none retrievable through /entitydata). Whatever Searge did must have been internal to a degree where the change isn't visible in vanilla. I think the issue you're talking about now is the same as my comment on MC-80778: WitherSkulls and SmallFireballs move jerkily/teleport unless the "power" tag is set just right. Not technically a bug, but I'd still like to see it fixed since it doesn't happen with big Fireballs.

Still present in 15w46a, reproduced using the same commands as in the video in the description.

Relates to or partwise contained in:

• MC-81659 (maybe)
• MC-77601 (maybe duplicate of MC-81659)
• MC-80142

Also MC-80778 seems similar.