This wasn't the issue, however, your post "triggered" me into figuring it out! I have a VKB NXT with a two stage trigger. I had the first detent mapped to gun/rocket fire, and for some reason the second detent mapped to bomb release (it should have been mapped to the red pickle button, so not sure how I managed that). Anyway, apparently the "bomb release" will also fire the missiles, so when I was pulling the trigger fully, it was firing one missile, and then a second missile. Moving the bomb release off the trigger solved it, so thanks!