If it's only 2nd it's likely worn dogs/windows on 2nd gear and the 3/4 cluster...have a strong mate come over and hold your bike upside down so you can just pull the lower case off to replace the gears.... shouldn't take any longer than say 3 or 4 beers to fix
I thought I read a while back the older ones had a detent spring problem, they would break or something, and they held it up in gear with their foot and it would stay in gear, could that be the problem, I'm not a mechanic just a thought.
See if you hold it in gear does it stay in gear, a broken dog won't hold I don't think, guess they fork can be worn and not putting it in all the way. Just a thought, and don't crucifie me if I sound like an IDIOT!! Jack of all trades, master of none



And yes I never heard of a safety situation you would want it to pop out of gear, what if you're pulling out into traffic and it pop's out of gear¡! You're toast, I would get a lawyer involved, maybe send a letter to corporate office Triumph stating the situation and threaten to get a lawyer involved, and if you don't hear back from them in a week or 2, got any lawyer's in the family, friends!!!! What are friends for.
That would be like saying the motor automatically shuts down and the brakes are locked to protect against any possible damage to the product, the bike does have a limp mode where if it's an immediate major problem, the MIL, or check engine light will come on. I've never seen that happen, but I know the computer will do that. But taking it out of gear when you are revving up the RPM's will make you tear a dog off the gear, not much different if you were to rev up the RPM's and kick it into gear, those dogs are coming off, and I don't know if you have to split the case's, but it's a whole lot of work taking apart a tranny. GL make them pay, and if you're still riding it, make sure you're significant other knows what's going on, just in case you pull out in traffic and get run over by a semi, at least they can live a good life, don't worry you probably won't even feel it, if it happens again, try like h*** to get on the shoulder!!! Of the road that is.
All kidding aside, be safe, and don't pull out in heavy, fast, highway, traffic, GL