lbgsloan, I guess I'm not really sure what you are talking about. The mission screen itself will not "show" a planet, i.e. I cannot bring up a planet and look at the grav well and see all the ships moving around and the defenses.
Now, if you are saying a planet will appear on the list of planets to target, well yeah. But that's not exactly "scouting" the planet! Your term is misleading.
This is probably not a bug at all, i.e. it is intended behavior. If people don't like it, I guess one "fix" would be to always have all planets appear in the mission screen. Then if you give a mission to a dead planet, it is your fault and means you didn't scout it.