Thanks for the report RedPiano. The timing is coded such that it is not supposed to happen, but obviously it did. I might even have an idea why. This can happen on any mission type if the timing calculations are not good. If you had two formations spawn independently at the same time and same place - right above you - then that is a pretty remarkable bit of bad luck
P.S. If you have it please save the mission file. Being able to look at it might help me to resolve the issue. Also, what density settings are you using - low/medium/high?
P.P.S. this section of code was not altered in 10.3. It could happen with any post 9.x release.
P.P.P.S. Until I manage to review the code think of it as an instance of not being aware of the Hun in the Sun