This sounds weird, but since Opera's default w (Wikipedia) search engine always directs to Finnish Wikipedia (which should be something you can change, by the way. My Opera installation's language is actually set to English, but it still goes to Finnish Wikipedia since I'm from Finland.)
So I've created a custom search engine, we, which directs to English Wikipedia like this: https://en.wikipedia.org/wiki/Special:Search?search=%s as the address.
Sometimes, when I've just started Opera, and I have a new tab opened and I start writing "we something", before I've finished typing it changes to "g something". I know this sounds like a real freak bug, but it has happened many times.
I can try to capture it on video if that helps.. if nothing else, to prove I'm not crazy
Edit: Here's my browser ident if that helps: "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.53 Safari/537.36 OPR/28.0.1750.31 (Edition beta)"