The bug
I don't know if this has any effect on the game play but the hitboxes of fireballs and wither skulls (subclasses of net.minecraft.entity.projectile.EntityFireball) are only visible every 3 seconds.
How to reproduce
Press
F3+Bto show the hitboxesSummon a wither skull
/summon wither_skull ~ ~ ~ {direction:[0d,0d,0d]}
Code analysis
Based on 1.12 decompiled using MCP 9.40 PRE 1
It appears the reasons for this are that constructors EntityFireball.EntityFireball(World, double, double, double, double, double, double) and EntityFireball.EntityFireball(World, EntityLivingBase, double, double, double) set accelerationX, accelerationY and accelerationZ (power NBT tag values) to NaN.
Additionally these values are not sent to the client after they were read from NBT server-side.
Comments
marcono1234
Close it completely or leave it open. If they only fix one of the bugs you can close it now.
The part which might be a duplicate is rather about the problem that the direction tag is needed
kumasasa
Is this still an issue in the current Minecraft Snapshot 15w49b or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
marcono1234
Reduced the report only to the wither skull hitbox problem, other parts were fixed, expect fire, but that was probably invalid or WAI
Confirmed for 1.13.1.
the two are indeed duplicated by this, also for the fire problem, paste it in the comments there as it's a fix, witherskull that's indeed an issue, not sure if reported yet
further more, please submit one issue per ticket