How to remove specific URL from Opera address bar autocomplete?

Opera 48 now seems to allow you to delete URLs from the address bar's autocomplete.

From http://blogs.opera.com/desktop/2017/09/convert-measurements-currencies-time-zones-opera-48/

Clean up unwanted suggestions

The autocomplete feature can be helpful when we regularly visit (or can’t quite remember the complete address of) a particular site, but there can be some entries or suggestions which we want to get rid of. For Windows and Linux platforms, Opera 48 allows you to delete URL history suggestions for web pages or search entries from being completed in the combined search and address bar. Whether that’s a mistyped search or a page you want to forget about, you can now get rid of it with just one click.

Deletable search or page URLs will have an ‘X’ on the far-right end of the entry in the search and address bar dropdown menu. No longer will you have to dig through your history log to delete these entries.

If you have bookmarked a URL it won't be deletable. I have occasionally seen non-bookmarked URL's that appear to not be deletable. I'm not sure if this is a bug, user error, or some other quirk.