No. The decryption is necessary if you want proxy-compression of HTTPS requests. Opera Mini is a proxy browser: everything you request goes through one of their servers (meaning, they know your every request and could read all of it) so those servers can do some compression and save you bandwidth. Sometimes only HTTP will get compressed, but here Nokia's browser will compress everything for you, including HTTPS. The issue isn't so much that they do it, but that this is a default browser and doesn't say this very obviously to users.
If you trust that proxy, then you'd be as secure as before, though I suppose every time you add a party to a communication line, you increase security risks.