Hey Peter,
First let me start by saying that you are 100% correct and that the issue are the two sidewinders. Once they are released the plane levels again.
Now, my only question is that has anything changed recently? because I never until now had a need to trim right off the bat at the beginning of a mission. As in, it almost felt like the plane has been trimmed already. Maybe its just my imagination but a large number of my flights start airborne to save time and I could bet my left testicle this behavior wasn't there before.
As far as trim is concerned, I'm aware of how it works ;)
It's no biggie really, just curious.