Unfortunately, the very reasons that make Opera dial-up friendly also make it somewhat incompatible with certain features. It's kinda meant for a more truncated web experience, less memory drain and whatnot. Which is why the Wii uses it, since there's not much memory to dedicate to surfing the web since it does so much and maintains a lot of its own data. I think the fact that you're ok turning off Java seems to indicate Opera has some compatibility issues with Java.
We had to talk about the various browsers in my Multimedia class, since you have to take how each one works in to consideration when designing a website. o.o
The only thing I can suggest is to check Opera's website and see if they have a patch relating to Java. ;/
