Well you didn't explain that in the first post.
What you can do is press Alt+Enter after you type your query so it'll load in a new tab, then you can go back to the previous tab and edit the previous search term and/or switch to another search engine.
I know this isn't the best it could... But at the same time I don't see spending resources on adding a dedicated search box as something very worthwhile.
To me Opera is telling their fans that either use the browser the way it is or don't use it at all.
As every other browser vendor does.
It's always about a choice. Some browsers have features Opera doesn't. Some browsers don't have all the features Opera has. You have to chose the one that fits you best since the WWW has been invented.
Just a note. It doesn't make sense to post this kind of topic in beta/dev sub-forum. You should have went with the "Suggestion box", or the Windows/Mac/Linux if it was a question. I'm moving the topic.