According to a post on the Battle.net forums a user has uncovered an exploit that supposedly gives players using the Wizard class in Diablo III temporary invulnerability. Blizzard has not confirmed that this exploit is real, for the record.
While we won't repeat the exploit here (you can read about it on Battle.net), it only takes five steps to make the exploit work, according to the poster. Some in that same thread have claimed to have had some success recreating this exploit, while others can't get it to work.
The exploit was posted by a player who claims that he (or she) was "unable to write a support ticket." If true, one could categorize such a bug as "game breaking." The exploit also supposedly works in all of the game modes. The only plus side to this story is that the exploit requires perfect timing, which makes it more difficult to replicate... The downside is that those foolish enough to use it may find themselves flattened by the all powerful Blizzard ban hammer.
Source: Player Attack