You're in a big battle on The Lost Temple, your Marines are battling to the last with their Gauss Rifles, trying to pierce through the Hydralisks' carapace. The battle is intense, as the Marines get support from Siege Tanks, and the Zerg brings in a dozen of Lurkers. And just when you think your Marines are about to make it, your Siege Tank lays the final smackdown with its Arclite Cannon, which kills the lurker. But at the same time, your Marines gets killed, because of the Lurker's last strength, giving double the damage. Familiar?
Probably seen it before
"Many people (including me) have probably seen it way before, it's probably as old as lurkers are." writes

This first screenshot is right before the Lurker attacks. Earlier it has been hit by the Siege Tank two times, which means that after the next shot the Lurker will be dead.

The second screenshot shows when the Lurker gets hit by the Siege Tank. At the same time, he attacks with his subterranean spine at the Marines, who now have received 20 hit points of damage. This is how it's supposed to work.

But if you look at the third screenshot, you see that the Marines die. How is that possible? A Lurker is only meant to do 20 damage. This is what the bug is about. When the Lurker dies and attacks at the same time, it deals double the damage. Is this supposed to happen? Did Blizzard intend the lurker to have the dying power? Was it by purposeful design? Does the Lurker all the sudden become a lot stronger the second he dies? Nevertheless, it's not logical, and should be considered a bug.

However, this can not be considered an illegal bug, since you can't do it manually. Blizzard will have to fix this in the next patch, if one ever comes out. This bug was originally posted at Progamer.cz by

You can check their article here » Progamer.cz.
The other bug mentioned in their article is zealot tango bug mentioned by

Links
WGTour.com - Source
WGTour.com - Download the replay here