As a pilot, I guess I'll offer my input here.
Mounting the AIM-120s on the wingtip rails does seem odd (our CF-18's are loaded with the AIM-9s on the tip rails), but in reality, it won't affect the flight characteristics of the aircraft to such a degree that the pilot will have trouble maintaining straight and level flight, and if you're close enough that you've got to pull excessive G's, you'll have already launched your 120's
This is due to the Fly-By-Wire control systems in the aircraft. Gone are the days where the stick and rudder are attached by rods and wires to the control surfaces. Nowadays, pilots are assisted by computers in flight (pilot pushes stick left, computer tells plane to roll left, etc...). Computers also control the trim controls which allow an aircraft to maintain unassisted level flight, and are always self-adjusting to do so.
As far as tactical gains go...c/Commander has a good idea. The 120 is a standoff weapon, so the pilot is most likely to use those at the maximum effective range in order to minimize risk to themselves. That'll keep the COB (Center of Balance) closer to the longitudinal axis so when one of the 9's is launched, it won't offset the aircraft at a critical time.
...or we could all be completely off, and some ground crew screwed up on weapons loadout.