It would seem to me pointless to show the on-screen keyboard when a physical keyboard is present. If someone were running Opera on a Surface or other x86 tablet and didn't have a keyboard - sure, I could see using the screen keyboard then. But sounds like they may not be checking for a physical keyboard when touch is used to focus the text area.
For now, you may want to go to https://bugs.opera.com/wizard and file an official bug report ... developers don't always read the forums.