Thank you for the reply, sgun. This is an unfortunate omitance of such a nice feature and usability experience, IMHO. How I wish Opera would at least add a preference tick box for this feature in an update even if they'll prefer to leave this unticked as default if they deem fit.
Now for some strange reason, after I enrolled in an Adobe Online Course where I used my Gmail, the password field of my Gmail has been clear even though I had Password Manager saved my pw in the past. Sigh.