This seems more of an anomoly than a bug, so I put it here. I'm sure Pyro will move it if needs be

Build a mission.
Advertise it.
Watch the pilot slots fill up.
Issue the mission text and RW channel.
Go through the comm checks and pre-launch banter.
Advertise the remaining few slots and time to launch.
Launch.
Listen on RW as one third of the mission takes to the air while you're still staring at the map room/clipboard.
Finally get on the runway and thumb the starter, seeing half your flight about 3-4k ahead of you and a couple saying on RW they're still in the map room waiting to launch.
All flights scheduled to launch at the same time.
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This started somewhere in 1.05. I'm sure most folks can recall the effectiveness with which Zigrat and myself used the mission planner in earlier versions

My first thought was maybe the in game clock speeds up a hair the longer you're in the arena, but I'd imagine that could only be it if the in game clock is client side (and I have no idea if it's client side or server side).
I've heard of people launching as much as one minute before others. I've launched and looked back to see kites in the mission have thier icon's disappear as I climb out and get farther than 6000yds from them.
Not that big a problem for the vets who coordinate everything anyway, but for some of the newbies using autolaunch it can/will seperate flights and increase the coordination work load in flight.