I have problem changing the password of my opera's account with Opera browser and i had to use Safari for that.
is it something that happens only to me?

Not at all. I can't change my password, so I can't get a new password to replace the old password that I can't change. To change the password, I need to give my old one - which is the very thing I can't do. The odd thing is, Opera was happy enough to accept my old password before. Crazy. And a reason not to bother w/ Opera