I'm adding this to the pile because apparently it's been around for almost a decade.
Using alt+drag on locked layers will cause them to duplicate like unlocked layers. I think this has happened to me before but I just noticed it now. Regardless, if you guys would like this to be a feature, just add the option to toggle it off in the preferences becuase otherwise, It's inconvenient as all hell.
I would like to not duplicate my locked background layer everytime I just miss the element I'm trying to click or worse, when I try to duplicate something underneath my locked vingette layer.