I think Opera's help and related information should indicate this "other bookmarks" area, or, even better, when the user sets up sync, the user is offered a choice of (a) this new machine will match the other exactly, in bookmarks, speed dials, or whatever you choose; or (b) we'll take the other machine's information and place in a separate area. Something along these lines.
After I set up sync on a new environment, I leaned back and waited for my speed dials to magically change from the default to the speed dials set up on another computer and when it didn't happen, I figured something was broken.
Now, to move SDs from the "other" area in the main. . . .