Strange Discovery: Playing with DatEdit

I was playing with basic modding with StarCraft: Brood War (that old game!), when I discovered something strange.

I set the cooldown of the Zergling's attack(Claws) to 30, which made it attack twice as slow as the Ultralisk(Kaiser Blades - cooldown 15). Surprisingly, after researching Adrenal Glands, the Zergling attacks not 33% faster, but twice as fast. Yes, its attack speed matched that of an Ultralisk.

So why does Adrenal Glands increase attack speed by 33%(cooldown is 8 before upgrade, 6 after) in Brood War? Turns out there is at least 5 in-game ticks of delay hardcoded into the Zergling animation (iscript.bin decompiled with IceCC). That, along with the time spent on displaying frames, playing the hitting sound, and processing the damage dealt to target unit, etc. limits the Zergling's minimum attack cooldown to about 5-6 ticks.