Extra Little Sister Bug

In the Neptune's Bounty/ Fort Frolic level, there are supposed to be 3 Little Sisters. But, if you are lucky enough you could be presented with a 4th Little Sister and Big Daddy combo shortly after killing the 3rd.

When attempting to exit the level the player will be presented with a message informing them that they have missed one or more Little Sisters........even though they got an extra one.

Fear not Xbox 360 acheivment junkies, this will not effect the "Little Sister Saviour" acheivment and you will still be presented with the 100 gamerpoints that you crave so badly.