@Swekob
Sure, I can understand that. But these fireballs are well within melee range. Stationary fireballs seem to be unaffected when spawned with no velocity data tag, but fireballs with velocity (all fired from a Ghast) are affected. While it is POSSIBLE to reflect the fireballs at close range, it's extremely unreliable to do so.
Originally, this bug came about due to the Singleplayer-Multiplayer merge, and I believe that may be the root cause, as it was not present beforehand.
Thank you Alexander for the helpful video.
Yes, it appears that this bug was fixed, at least as of 16w40a. Could be a result of the reworked data tags for Ghast Fireballs in that snapshot, but either way, this bug is finally resolved.