Ah good thing you metioned that, Chewi. I noticed the same thing, only I had my salvo set to 3. I also did not have formation, as I never fly the 234s with the formation. So I dropped my eggs on the town for easy perkies. I totally forgot to reset my salvo, but when I selected the RATOs, the contrails were indeed missing.
But I think the contrails were missing for an entire different reason. I dont have a good graphics card. My computer is at least 7 years old, with the integrated graphics. I run on default graphic settings and sometimes smoke doesnt appear when it should. IE: flak and clouds are glitched sometimes. Engine oil smoke, and even the contrails are glitched. I notice that when I look at the smoke at a certain angle, it appears in full. But if I look at the smoke at another angle, it dissappears entirely.
Your problem may be an entirely different issue, but it appears it may be a graphic glitch rather than a real bug per say...