What is curious is that it took them a long time to find. I’d think that -as long as you believe there is a bug- this should be fairly straightforward to spot.
People blamed this behavior for everything from loot drops, to combat outcomes, and to aggro mechanics.
And also remember that AC was before MMOs became massively popular, and outside of specific events and locations, there wasn't always more than a handful of players in a certain area for a given server where aggro mechanics like this would matter.
This is the power of continuous integration.
There's a certain amount of optimism needed to keep going as a software developer, and then there's the crippling amount of optimism that a lot of people have which makes for difficult team dynamics. CI says it doesn't matter if it works on your machine, it's red on a neutral box so fix your problems or it's not going into the release. It's much harder to ignore Jenkins than to ignore David.
People learn through trial and error that the Wally Filter works on bugs, so denial is their first and best defense. Prove to me there's a bug. I won't spend any time on it until you do.