However, reddit's markdown handling doesn't require you to do that. Neither does stackoverflow's. They know the( and ) in this case are part of the URL, especially since there's no use of the () syntax in this case.
But, even with the () syntax, stackoverflow knows the ( and ) inside the URL itself are part of the URL and not a delimiter/opener/closer for the link syntax.
Stackoverflow's and Reddit's handling just seems to be more robust.
Stackoverflow uses the StackEdit editor that uses the pagedown markdown converter. They're both open source.
In my opinion, many users have problems about lost data which they post on the myopera, although Opera inform to users about deadline to close Opera. In this case, Opera should support for the users. The user used Opera many years before. Opera should consider these.
AFAIR only the past 6 months were imported. The rest would be outdated anyway, wouldn't it?
No, it would not be outdated. Opera 15 is about 9 months old, but many users are still using Opera 12 or earlier versions. You may as well import all of the old posts. There's gold-dust in some of those old threads about customising Opera, fixing plugins, etc.
Although 90% of the threads are not worth importing, the 10% that are should not be lost to the community. Perhaps you could import all threads from the important forums — Windows, Browser, Mail, and Customising (and some others) — except those that were locked?
It is probably easier to import the whole lot rather than filtering out some.