When I drag a layer mask to the trash, it applies the mask instead of deleting it, removing all masked out pixels. I don't believe this was the case before CS6. Is there a way to adjust this setting and make it simply delete the mask?
Right-clicking still gives me the option to delete the mask properly.
You should see the following dialogue unless you've previously ticked "Don't show again". I guess you ticked that when recently applying a mask.
I don't know how to make the dialogue reappear, except by resetting the entire Photoshop preferences.
Edit: at bottom of Preferences > General is "Reset all warning dialogs". Maybe that'll bring back the dialogue.