Snapshot 13w06a, Minecraft 1.5, Minecraft 1.5.1, Minecraft 1.5.2, Snapshot 13w21b, Snapshot 13w22a
Jre 7 x64
Running standalone server
When the command block is used on players with one of the selectors, it will perform the command on dead players who are still in the respawn screen as well.
In any game where you need to award a player for remaining within a region, they can simply die and sit there, and they can not be removed as there is no way to determine if they are dead or not. This opens up a simple way to cheat at many kinds of custom maps.
It would be nice to simply have a flag for it, that way we could simply only select the living, or intentionally select the dead.