This conversation has been merged. Please reference the main conversation: Photoshop: alt+right click drag resize opacity lock
Now, when there is no such an option to permanently lock this settings - there is a chance to mess this settings by accident and all work is ruined (specially when you change opacity to 99% and after masking all object, you discover that all masking work is messed.)
And this changing by accident is very simple to do - just change size of brush (in a rush) by alt+right mouse button + drag left/right, and move mouse slighty up/down by mistake.
I hope my idea is clear.