Alternatively, I guess it's feasibly possible that a person could have accidentally altered the Game Interface value for the hero death message and put in a variable that wasn't designed for it.
That happens sometimes when you load and save two or more maps in one session of World Editor...Ive seen object data get overlayed with eachother and mess things up bad. Easy way to prevent this is to close world editor every time you change maps.
But check the Interface constants under the advanced tab. Go down to the text section and check the string that applies for when heroes are killed. -VGsatomi