No, definitely not good practice. It had seemed fine when I adjusted it, I don't go for hair triggers. I was quite surprised when it misfired like that. I was always loading whilst the gun was pointed down range fortunately (especially careful after first incidence). I have backed the adjuster off now and have tried to make it fire again by forcefully pushing the cocking device home and haven't repeated it so I hope that is the end of it. The trigger is still a bit heavier than I would like though.
I was initially worried I would need to return the gun.