Posted by dOoBiX on January 22nd, 2012 at 1:16 pm | 12,111 views
HuskyStarcraft has posted a video up showing that it is possible to stack Siege Tanks, as well as other units like Thors, by dropping them in tight spaces with Medivacs. This was originally discovered by DerNalia, who was a victim of this attack in a game, and had posted a screenshot of it on the reddit StarCraft forums. Blizzard will likely fix this bug in an upcoming patch, as they have done so with these types of exploits in Brood War.
HuskyStarcraft has also made a 2nd video showing tank-stacking with buildings here.
Big update: HuskyStarcraft has posted a 3rd video of the same bug, but this time some people have figured out how to get the tanks to fall off the edge of the cliff and move around at the bottom of the map! Check out the exploit in the video below: