Interesting. I have a '56 94 that I shoot a fair amount and I have never experienced what you are describing.
So if you hold the lever it does not happen but if you don't, it will open when fired right?
How do you hold in the safety interlatch that is right behind the trigger if you don't keep your hand on the lever?
10mm and 357sig, the best things to come along since the 38 super!