The issue the OP noted has been occurring since last February/March... it is an opera issue.
If anything, Opera is sand-boxing the downloaded container when a user executes the container within opera downloads.
There's nothing to be concerned about, just delete the scopeddir* folder and it's contents. The original file you downloaded will still be in the location you downloaded the file to.
The contents of the scopeddir* folder is just a copy of the original file you downloaded, explicitly when you executed the file through Opera.
That's the thing, it's been almost a year this thread has been created, and I myself remember using a bug report form twice...
Yea we know we can just remove these directories, but it's not something we, users, should be doing... Especially when you're downloading a lot, then you may get confused about why is the size of the downloads folder doubled.
I really wish an Opera developer would at least tell us if the problem was acknowledged.