After a little more testing I found it only does this if you use the keyboard shortcut. Weird. So, if I have "w chicken" in my clipboard or I have "w " already in the address bar and "chicken" in my clipboard and I right click the address bar and click "Paste and Search" (which has CTRL+B next to it in the menu) it will take me to the wikipedia page for chicken. Interestingly, if I have "w chicken" in my clipboard and I just type Ctrl+B it does a google search for "w chicken". It seems the keyboard shortcut doesn't share the same functionality as the mouse right click menu and just passes whatever is in the clipboard directly to your default search engine, ignoring whats in the address bar or your other search engines completely.
Opera for Windows