I'm currently trying to port my Chrome extension Prime Player to Opera. It uses the chrome.omnibox API which should work exactly the same way as in Chrome according to the spec.
However, it seems that the results are sorted alphabetically (by description of SuggestResult) in Opera. This is not intended because I would like the results to be presented in the order as they are provided to the suggest callback (provided to the onInputChanged callback). Since only the first 5 results (after sorting) are displayed, more important results might not only be displayed later, but they even might be missing completely.
Conclusion: The results should not be sorted, extension developers should (be able to) order their results by priority themselves.
I know, this is not a real question, but there's no other possibility to report bugs regarding Opera extensions than a question tagged with "opera-extension".
To verify the behavior, you could just download the sample extension mentioned at the end of the tutorial, unzip it, edit the 2nd result's description from "Do a Stack Overflow Search" to "Stack Overflow Search", load this as unpacked extension and see that "Stack Overflow Search" in Chrome is the 2nd suggestion whereas it's the 3rd suggestion in Opera (because it is sorted behind "Search on Google").
You can actually report bugs directly: https://bugs.opera.com/wizarddesktop/
Re the problem - it seems to me utterly logical that the order set by extension should not be sorted. I believe that setting the alphabetical order is a default behavior of address bar suggestions and there is no any exception for extensions implemented inside. I reported the bug in our system.