I replicated the problem with a new project, with the simplest instructions ever. I added a sprite, then deleted it -- in the Objects tab on the side, it's gone, but if you go to the event sheet and start adding an event, you can see that there's three previously deleted sprites in the "Add event" box.
db.tt/PjH7X90P
Of course, this seems to be a little... too simple. If no one else noticed this it might just be a problem with my computer. <img src="smileys/smiley5.gif" border="0" align="middle" />