the fact that you can schedule a conflicting reservation is a bug.
Actually, building schedulers are allowed to create conflicting reservations in the calendar. This seems like a bug but is actually not logged as such. The help does state:
Although the calendar doesn't allow calendar editors to double-book the same location at the same time, the same rules don't apply to building schedulers creating reservations. When you schedule a reservation, you are not alerted about any conflicts with other reservations or events.
I'm not sure why the calendar was programmed this way. I'll log it as a bug, but rather than fixing this, I think it will be addressed with the revamp of the way reservations works in the calendar. That update is coming but I don't have specifics yet, as the teams were focused on other things toward the end of 2012.