Votuko

So was everything to do with players colliding with other players a bukkit feature?

For example I remember that it used to be possible to nudge other players in multiplayer, but it was removed at some point.

I had been pretty sure that that was at the same update that reworked player code and caused this bug, but seeing as this bug apparently never existed I am beginning to doubt my memories. (I was sure I remembered reading a Mojang post about collisions being reworked to require a non-zero damage value to trigger, thus breaking any item that previously had knockback but zero damage. At that point I wouldn't have been reading something by bukkit...)

This may not be very helpful, but I believe that the bug originally appeared around version 1.3, when a lot of player collision code was reworked.

It was in the same update when players lost the ability to nudge other players on multiplayer, as well as when all items that deal no damage (snowballs, fishing rods, eggs) lost their ability to knock back players as they previously could.

I'm not set up to check the game myself, but there are plenty on anecdotes on the Minecraft Forums of people talking about how snowballs used to hit players. (Not to mention the number of duplicate reports of this bug on this site!)

TL;DR I'm not sure why this is being debated, because the bug is clearly marked as "confirmed". That was done by a mod who knew the game at the time, with the consensus of all those who reported it.