Well I run my own proxies at times and I can tell you that Opera never bypasses your proxy settings. Opera Turbo should of course be off. If an anonymity checker is reporting your real IP and you have a proxy enabled in Opera, I guarantee it's because the proxy is leaking information, not Opera.
I respect your opinions but, and again with all due respect, there are better techs than I consider you to be who have said different. As far as Tor leaking information to the proxy checker sites? not possible or they would have done so with Firefox.
You did not mention by the way:
To NEVER enable "Opera Link Synchronization"! It stores your data online on an Opera server!
or
To NEVER enable "Opera Unite"! It exposes you as a server. Also uncheck "Discover local Opera Unite Users" in "Tools"->"Opera Unite Server"
or
Go to: "Tools"->"Preferences"->"Advanced"->"Security":
UNCHECK "Enable Fraud Protection". Otherwise every domain-name you visit will be sent to an Opera server!
The basic standard for loading a proxy in Opera should be:
Go to: "Tools"->"Preferences"->"Advanced"->"Network"->"Proxy Servers...":
CHECK all protocols and make sure that you put a proxy IP and port in each field.
Only the HTTP proxy has to be a working one. The others can be bogus and don't need to be functional, but this will prevent a proxy-bypass attack by blocking direct connections to a remote server for these protocols.
I do not know for sure what went wrong when I installed the new updated version of Opera and frankly I do not care. The browser was just not built to be "anonymity friendly" nor are the developers leaning in that direction, quite the opposite. So I switched, you and others are welcome to do as they please with my blessing.