Not that this has a direct application to what you have, but might give you an idea how/what the makers were thinking...
I have my Grandfather's Ithaca 12ga SxS that he had made to his order (stock. barrel length, chokes) in 1909.
Double triggers (of course) and it has a 3 position safety. Other guns of that era I have seen don't.
Center is safe, forward is fire, and if you break open the gun, it moves from fire to safe.
However there is a third position, all the way back, the gun is on "fire" and it does NOT go on safe if you open the action.
O/U guns are often used for trap & skeet, it is entirely possible (and I think likely) your gun was originally, and intentionally made so that the safety was NOT automatic when the gun is opened.
People often thought in different terms back then, and I think Ithaca figured it was perfectly fine the way they made it. If you wanted the safety on, you put it on. It didn't go on by itself, possibly getting in the shooter's way. Missing the next bird or clay pigeon because the safety put itself on, and the shooter didn't realize it was a worse "sin" than the tiny risk of not having the safety on, until the shooter put it on.
It is possible the gun came from the factory with the automatic safety and some previous owner had that feature deactivated, I don't know that model gun well enough to say, but I think it most likely it didn't come with the automatic safety. Its possible that back then the automatic safety (going on safe when the action is opened) was an option, and the gun was simply ordered without that option.
Its not as flaw, its a feature.