The search bar is still as wonderful as it was when this thread was started. You cannot type anything into the search bar that starts with y, d, z, b, or w, or it will start searching Yahoo, Duckduckgo, Amazon, Bing, or Wikipedia. Fortunately, since Google is my default, I can type anything that starts with "g" without any untoward behavior. I thought my browser had been hijacked the first time it happened, because I was trying to get to a website that started with "z" and it kept searching Amazon. I love Amazon, and go there all the time, but it's not the only website in creation.
What version of Opera are you using? In v. 32, when I type in the search/ULR bar (is that the one you mean?), if I type, for instance, "yerba buena" or "zoominfo," it uses my chosen default search engine (DuckDuckGo) to search for those terms. It only goes to Yahoo or Amazon if I type a y or z followed by a space.