I have an Omnilite stove, which uses either a canister or white gas with a pump and bottle. It uses the same Lindal valve for both. With white gas, I almost never disconnect the stove from the bottle, and I've never had it leak in my pack. Again, that's with exactly the same valve that would seal a canister.
I rarely use canister gas with the stove, but when I'm not carrying it far, I do use 1 lb propane bottles via an adapter. I have had those leak in my pack, but only when not connected to anything. Ironically, the solution to stop the leak was to thread the bottle onto the valve.
The other thing I learned with leaking propane in my pack, is that it would take many hours for the whole bottle to leak out.
I have had a stove leak white gas inside my pack. It was an older stove, and the O-ring fell out of the fill cap and I didn't notice. Despite the tank leaking nearly to empty all over my pack's contents, the only thing that wasn't fixed by a couple hours of sunlight was a bag of roasted corn snacks, which didn't smell like white gas, but had an odd gas aftertaste. Years later, we still joke about that trip.
Lessons learned: it may be better to leave fuel bottles connected to valves inside packs, but stove fuel leaking in a pack isn't as big of a problem as it seems.